MEXICO CITY A gray Suzuki stopped outside the General Hospital of Mexico and deposited a heaving Victor Bailn at the entrance. He had refused to come to the hospital for days, convinced that doctors were killing coronavirus patients. By the time he hobbled into the triage area and collapsed on the floor, it was too late.

Papito, breathe! his wife screamed. Please breathe.

Within an hour, Mr. Bailn was dead.

Mexico is battling one of the worst coronavirus outbreaks in the world, with more than 52,000 confirmed deaths, the third-highest toll of the pandemic. And its struggle has been made even harder by a pervasive phenomenon: a deeply rooted fear of hospitals.

The problem has long plagued nations overwhelmed by unfamiliar diseases. During the Ebola epidemic in 2014, many in Sierra Leone believed that hospitals had become hopeless death traps, leading sick people to stay home and inadvertently spread the disease to their families and neighbors.

Here in Mexico, a similar vicious cycle is taking place. As the pandemic crushes an already weak health care system, with bodies piling up in refrigerated trucks, many Mexicans see the Covid ward as a place where only death awaits to be avoided at all cost.

The consequences, doctors, nurses and health ministers say, are severe. Mexicans are waiting to seek medical care until their cases are so bad that doctors can do little to help them. Thousands are dying before ever seeing the inside of a hospital, government data show, succumbing to the virus in taxis on the way there or in sickbeds at home.

Fighting infections at home may not only spread the disease more widely, epidemiologists say, but it also hides the true toll of the epidemic because an untold number of people die without ever being tested and officially counted as coronavirus victims.

Many Mexicans say they have good reason to be wary of hospitals: Nearly 40 percent of people hospitalized with confirmed cases of the virus in Mexico City, the epicenter of the nations outbreak, end up dying, government data show, a high mortality rate even when compared with some of the worst coronavirus hot spots worldwide. During the peak of the pandemic in New York City, less than 25 percent of coronavirus patients died in hospitals, studies have estimated.

While the statistic may be imprecise because of limited testing, doctors and researchers confirmed that a startling number of people are dying in Mexicos hospitals.

During a surge of cases in May, almost half of all Covid-19 deaths in Mexico City hospitals occurred within 12 hours of the patients being admitted, said Dr. Oliva Lpez Arellano, Mexico Citys health minister.

In the United States, people who died typically made it five days in the hospital.

Doctors say more patients would survive if they sought help earlier. Delaying treatment, they argue, simply leads to more deaths in hospitals which then generates even more fear of hospitals.

The distrust is so pronounced that relatives of patients in Ecatepec, a municipality outside Mexico City, stormed a hospital in May, attacking its employees, filming themselves next to bags of corpses and telling reporters that the institution was killing their loved ones.

After seeing videos of what happens to people inside hospitals, screw that, said Mr. Bailns brother, Jos Eduardo, who had recently spent 60 days at home recovering from his own bout with what he believes was the coronavirus. Id rather stay home and die there.

But many people who die at home in Mexico or even on the way to the hospital are never tested for the virus, so they are not counted as coronavirus victims. Instead, they fall into a statistical black hole of fatalities that are not officially tied to the pandemic.

Even by the official count, Mexico has already suffered more coronavirus deaths than any other nation but the United States and Brazil. And the government said recently that during a period of over three months this spring, there were 71,000 more deaths than expected, compared with previous years an indication that the virus has claimed many more lives than the official tally suggests.

Adding to the confusion, political leaders here, as in many countries, have sown doubts about the virus and the need to seek medical care. The hugely popular president, Andrs Manuel Lpez Obrador, said he uses religious amulets and his clean conscience to protect against the coronavirus, and he has advocated fighting the pandemic at home, with the help of families, rather than in hospitals.

Nearly 70 percent of Mexicans said they would feel unsafe taking their loved ones to the hospital during the pandemic, in a survey published last month. A third said they would prefer to care for their relatives themselves.

Now the nations top health officials have begun pleading with Mexicans to stop resisting medical care.

Its very important that late care doesnt contribute to death, Hugo Lpez-Gatell, the health official leading the countrys response to the virus, said at a news conference last month. Please, go to hospitals early, especially people who are most at risk.

Many are wary of the costs that come with a hospital stay. And in a country plagued by rampant government corruption, the fundamental distrust of the authorities often extends to doctors and nurses in public hospitals.

At the General Hospital in Mexico City, where Mr. Bailn died, suspicion was running high. No one had wanted to come to the hospital, a place that seemed to swallow their loved ones and leave them outside, with few updates to calm the nerves. Everyone had a theory about the real cause of the virus and the destruction it had unleashed.

Modesto Gmez, whose wife was inside, heard the government was letting elderly people die of the virus because they had expensive pensions. Hctor Mauricio Ortega, whose father was intubated there with a Covid infection, said he believed doctors were purposely infecting people with the virus because countries have a quota of people who need to die every year.

Ral Prez woke up in a panic on the benches outside the entrance. It was his 16th day sleeping there after his sister went in for brain surgery.

He said he had met seven families of patients who had come in for another illness and then died of the coronavirus.

Updated August 6, 2020

People think maybe theyre injecting them with something or killing them in there, he said.

Mr. Prez didnt believe the rumors at first, but then doctors told him that his sister, who was still intubated after her brain surgery, had tested positive for coronavirus. Now he was frantic, calling all of his relatives, telling them the hospital wanted his sister dead.

They are letting people get infected, he said. They just want to get rid of one more patient.

Dr. Lpez, Mexico Citys health minister, said that rumors of malicious medical practices had been widespread. Doctors were supposedly stealing the fluid from peoples knees, or trading their fingerprint data gleaned from oximeter readings.

There was a big fake news campaign spreading rumors that health workers were attacking people inside hospitals, profiting from their death, she said.

Dr. Ernesto Nepomuceno said that in his clinic in Iztapalapa, a poor neighborhood in Mexico City, doctors perform oximeter readings on themselves to show patients that they are measuring oxygen levels, not recording personal data.

We have to make great efforts to put people at ease, Dr. Nepomuceno said.

Two days before Mr. Bailn was wheeled into the General Hospitals intensive care unit, he visited a doctor in his tiny hometown an hour outside the capital. His oxygen levels were low, but he begged his wife, Fabiola Palma Rodrguez, not to drive him to the hospital.

Please dont take me there, I dont want to die, she recalled him telling her. By the time Mr. Bailn relented, he was already ravaged by the disease.

After a local hospital turned him away, he made the trip to Mexico City. He died on a stretcher in the General Hospital, Ms. Palma said, before doctors could intubate him.

I would have taken him earlier, but we were both too scared, Ms. Palma said. It is so unfair. I took him there alive and brought him back home dead the same day.

Aurora Arzate Nieves died on the same day as Mr. Bailn, in the same hospital, about 30 hours after being admitted. The matriarch of a tightly knit Mexican family, Ms. Arzate, 83, was known for her green mole dish and strong will. Her sons practically had to drag her to the hospital.

That decision was tormenting Eduardo Gutirrez Arzate as he said a final goodbye to his mother, who was zipped into a bag inside a Ford minivan converted into a hearse by a funeral company near the hospital.

Pawing at the window, Mr. Gutirrez begged his mother to wake up.

I felt really guilty when I saw her, he said, standing outside the crematory, black smoke billowing overhead.

She was scared of everything having to do with the coronavirus and of hospitals, where shed be surrounded by depressed people, instead of by her family.

I asked her in that moment to forgive me, he said. I asked her to forgive me for taking her to the hospital.

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Mexicos Coronavirus Struggle Worsened by Fear of Hospitals - The New York Times

Face masks and coverings come in many different forms. But are they all the same at preventing the ... [+] spread of Covid-19 coronavirus? Here Ashley Haas (L) and Heather Aboff are seen in SoHo, New York City, wearing theirs. (Photo by Gotham/GC Images)

Face masks can be like pizza, at least in certain ways.

People can end up wearing both on their faces, albeit for different reasons. Both can come in a wide variety of types and designs. And not all are created equal. Some (face masks, not pizza) are better than others at blocking droplets that may come out of your nose and mouth. In fact, some face coverings can actually make things worse, causing even more droplets to spew out into the air, according to a study just published in Science Advances.

Yes, you heard that correctly. Wearing some face coverings can be even worse than when you wear nothing at all. That isnt quite how the Alison Krauss song goes, so how then can a face covering possibly be worse than wearing nothing but the smile on your face? Arent face coverings supposed to block all that stuff that comes out of your mouth and nose when you do things like cough, sneeze, talk, sing, pant, and say, ohhh, pizza? Arent face coverings supposed to help block your filthy nose and mouth from transmitting the Covid-19 coronavirus to others?

For the study, a team from Duke University (Emma P. Fischer, Martin C. Fischer, David Grass, Isaac Henrion, Warren S. Warren, and Eric Westman) created some spitting images of a person talking into a box. The study used freaking laser beams to do this. The laser beams created a sheet of light inside the black box in front of a hole in the box. So, essentially the experiment wasnt just a black box.

Next, the research team asked a person to position his or her mouth at the hole and repeat the phrase, stay healthy, people, five times. Therefore, anything that would come of the persons mouth, whether its small droplets or hot dog fragments, would subsequently hit the sheet of light, causing the light to scatter. In other words, any droplets or particles would scatter the sheet out of it. A cell phone camera filmed this sheet show, which would allow the researchers to quantify how much stuff was coming out of the persons mouth.

The person repeated this procedure multiple times, first without any face covering and subsequently with 14 different types of face masks. The person didnt wear all 14 masks at once, which would have looked ridiculous. Instead, the person tried them one at a time. The research team established a relative droplet count scale with a 1.0 count representing the number of droplets that hit the sheet when the person had no face covering and 0.0 representing what happened with the best mask of the bunch.

A view of an N95 face mask outside NYU Langone Health hospital during the coronavirus pandemic. ... [+] (Photo by Noam Galai/Getty Images)

It should come as no surprise that the best mask was clearly the fitted N95 mask that didnt have an exhalation valve. After all, this is what health care workers are supposed to wear, assuming that their health care facilities actually have provided enough of such protection. These masks are designed to keep droplets and viruses from going either direction, out or in, and protect both the wearer and everyone else. Experiments with this kind of mask in essence kept the sheet together with not much scatter recorded. Indeed, such masks arent perfect. However, they served as the standard for this experiment with a relative droplet count of basically zero.

Surgical masks, like the ones seen here being worn by medical workers in Hong Kong, China, finished ... [+] second in the testing. (Photo by Qin Louyue/China News Service via Getty Images)

The second place finisher was not too surprising either. Compared to the N95 mask, the three-layer surgical mask had a more variable relative droplet count that ranged from zero to 0.1. These masks are medical grade as well and can be like boxers (the underwear and not Mike Tyson). They can keep most things inside but every now and then can let something sneak outside.

The third and fourth ranking masks were the ones with polypropylene: the cotton-polypropylene-cotton mask and the 2-layer polypropylene apron mask. These had relative droplet counts around 0.1, a little bit higher than the surgical mask.

The fifth through eleventh place finishers included four different two-layer cotton pleated masks and one one-layer cotton pleated mask. These fell in the zero to 0.4 relative droplet count range. So they caused some sheet to move around.

Does your N95 mask have an exhalation valve? (Photo: Getty)

Number seven was another type of N95 mask: one with an exhalation valve. This registered a relative droplet count ranging from 0.1 to 0.2. When using a N95 mask, check first whether it has an exhalation valve. A N95 mask with such a valve is a bit like those one-way see-through windows. It provides full protection only in one direction. While the mask may protect you, you can still end up exposing yourself to others. Let me re-phrase that. You can still expose others to whatever may come out of your mouth and nose.

The valve allows air to move from the wearers mouth and nose through the mask without going through the main filter. While this may make exhaling easier, at the same time, it may permit viruses to get on through to the other side. This exhalation valve may be fine if the sole purpose of the mask were to protect you from what may be in the air. An example would be working with construction materials as you are building your plaster Justin Bieber shrine. But such a mask wouldnt protect others from you as well as a N95 mask without an exhalation valve would. Thats why health care workers dont tend to use N95 masks with exhalation valves.

The ninth place finisher was a one-layer Maxima AT mask that had an average relative droplet count of 0.2 with its range going no higher than 0.3.

At number 12 was the knitted mask. Not surprisingly this mask had a pretty large range, going from a relative droplet count of around 0.1 to just under 0.6. A knitted mask tends to be like a politicians speech, full of holes. And holes can let a whole lot get through to the other side.

Then there were the two masks that could actually be worse than wearing no mask at all. At number 13, the bandanna had a range of 0.2 to 1.2. This suggested that going Axl Rose on your nose and mouth could in some cases allow more droplets to get through than when going bare-nosed and bare-mouthed. How could this be? How could a bandanna create even more droplets? Well, the answer is shear reality.

Depending on its arrangement, construction, and positioning, a bandanna may actually shear larger droplets into many more smaller ones. Think about the last time you try to push a block of Parmesan cheese through a screen window (because who hasnt tried that). Smaller droplets are worse than larger droplets because they can float in the air longer and may make it through a persons respiratory tract more readily.

The last place finisher showed why when purchasing a face covering, you shouldnt get fleeced. The fleece mask finished at number 14 on the list, worse even than wearing nothing at all. The experiments showed that you could still create quite a sheet storm while wearing the fleece mask. The average relative droplet count was 1.1. That means, on average, the person while wearing a fleece mask generated more droplets than when his or her nose and mouth were fully exposed. Like the bandanna can do in some cases, the fleece was making big problems into many more little problems. And thats not good.

Of course, this study was not perfect and had its limitations. It didnt test all possible versions of the different masks. Who knows what might have happened with different people who have different facial shapes and ways of speaking. Spraying droplets doesnt necessarily mean that you are spraying viruses. Each droplet may not contain enough of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) to infect others. And certainly stay healthy, people, is not the only thing that you may be saying around other people. What would happen, for example, if you were to say something like it is what it is?

Nonetheless, all of this is a reminder that public health recommendations have their nuances and associated detail. Its not enough just to cover your face. Covering your face with sweat, chocolate, pizza sauce, or shame wont suffice. And using just any mask wont do. For example, dont show up at a Costco wearing a Lone Ranger mask or a mask that doesnt really block whats coming out of your nose and mouth. Even when you are seemingly covering your nose and mouth, you may not be adequately protecting others. Therefore, be careful when choosing and purchasing a mask. Choose the right face covering. After all, you wouldnt say, just bring me some pizza, any kind of pizza, would you?

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Study: 14 Face Masks, Here Are The Best, Worst For Covid-19 Coronavirus - Forbes

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Testing has taken on a gigantic role in the story of this pandemic. Its the subject of genuine confusion and grandstanding claims, and because it provides the basis of our knowledge about the virus, its legitimately important. But its funny: despite how vital tests are, I dont think most people know how they work.

Lets address that. While were at it, lets also look at how long tests take in Utah, why testing numbers have changed in the state (its not a conspiracy), and what might be coming down the pipeline.

The vast majority of coronavirus tests administered in the United States are called RT-PCR tests. Basically, we want to know whether or not a person has the virus RNA in their upper respiratory tract. So we get a sample that could be saliva, cells from the nasopharyngeal tract (gathered with those long cotton swabs), or just from the nostril. From there, we use chemicals to break open the cells in the sample and filter it so we get just the bits that are the size of RNA.

To figure out what kind of RNA it is, we use a technique called polymerase chain reaction, or PCR. Weve known how to do PCR for only 35 years, but its become so important for so many applications that we did it in my high school chemistry class 12 years ago.

Basically, what PCR does is amplify the DNA in a sample from just a few copies to millions or billions of copies, simply by adding a number of ingredients into a test tube and changing its temperature.

For the coronavirus, we have to turn the RNA we sifted out of our sample into DNA by adding an enzyme called reverse transcriptase. Then, we add DNA polymerase to the soup, along with DNA building blocks, fluorescent probes and coronavirus-specific primers.

Then its all about the temperature.

We heat the mixture to 200 degrees to split open the DNA into strands, then cool it to 140 degrees. That temperature allows the primers to potentially bind to the open DNA, but only if they match the genetic code of the coronavirus. The probes attach too.

Then, we heat it up to 161 degrees. This is when the rest of our soup goes to work. The DNA polymerase assembles building blocks floating in the soup to recombine into that beautiful double-helix you picture when you think of DNA. The probes get knocked off the chain and begin to glow.

By repeating this cycle 25-35 times, we can turn one copy of this DNA into billions of copies. And at that point, the solution can fluoresce so much that it can be detected. But remember, it only will light up if the coronavirus RNA was there in the first place otherwise, the primers wont attach, and no copying will happen at all.

This is very impressive stuff, but PCR takes 2-4 hours and requires a specialized oven to quickly heat and cool this solution to the needed temperatures. It also requires a lot of specialized material: for example, the DNA polymerase has to be heat-resistant, so we get it from microorganisms that usually hang out near geothermal heat vents in the bottom of the ocean. Of course, we need those coronavirus-specific primers, too. This stuff can and has been subject to shortages in the pandemic.

How long does it take for people to get their test results back?

Of course, just because it takes less than a day to actually complete the test doesnt mean people get their results that quickly: samples have to be driven to labs, then prepared once they get there. Afterward, test results have to be recorded, sent to a medical provider, and then the patient has to be contacted.

Thanks to the Utah Legislative Auditor General, we now know how long this typically takes in Utah. On average, it takes 1.6 days from the time a sample is collected to when the lab notifies the medical provider.

While 1.6 days was the average, there was significant variation between labs. One lab got the results back within 1.3 days on average, but another major lab took 3.7 days to get the test results back. The labs werent identified in the audit, instead they were called lab A, lab B and so forth.

And there was tremendous variation in between individual tests, even at the fast labs. The quickest lab still took seven days on a few tests, and one of the labs that performed well even had a batch that took 21 days to process 21 days!

The audit found that testing times increased as labs dealt with more tests. It also found that tests outside of Salt Lake County were more likely to take longer, presumably because of the driving time required to get them to a lab.

We dont know how long it usually takes medical providers to tell people whether they are positive or negative. Sometimes, it seems people are contacted in a matter of minutes or hours. But sometimes, it takes longer than that: the audit notes that one major provider just stopped notifying patients who had tested negative in June and July when testing volumes increased.

Heres the issue: a coronavirus test that takes more than a few days to come back is nearly worthless from a public health standpoint. People who are tested are relying on the results to decide whether or not to quarantine themselves youd hope that anyone taking the test would quarantine, but the reality is that some will do the minimum until they hear the word positive.

Some businesses require a positive test before COVID-19 sick leave can begin, and nearly all businesses would wait until a positive test to inform close contacts. When theres a delay, all of those secondary interventions are delayed too, allowing times for the virus to spread.

The audit included several suggestions, all of which the Utah Department of Health agreed to work on. They want to set a goal for test processing times. They want to collect data on how long each test takes, and publish the results to coronavirus.utah.gov. They want the labs to share best practices and resources on how to get these tests done more quickly. And they want the labs to work together when theres a pileup at one lab and capacity at another.

Why has testing slowed in Utah?

Clearly, the number of tests performed has declined in Utah over the past month, as has the rate of positive cases.

This has led some to believe Utah is fiddling with the system intentionally reducing the number of tests taken in order to reduce case counts, making it look like the state is recovering when it isnt. This would be rather evil.

I dont see a lot of evidence for that theory, though.

Those who work at testing sites have noticed fewer cars driving through than before. It might be due to the heat, it might be because people are on summer vacations or because they are just less interested in getting tested. Those are all relevant theories covered by my colleagues Erin Alberty and Sean Means this week.

The biggest factor, though? I think fewer people are getting sick.

The past three weeks, the system has found pretty low levels of coronavirus in the sewers, much more comparable to the relative lull in mid-May.

I suppose its possible that the government is cooking the books on the numbers of tests performed, that they instruct random testing site employees to lie about drive-thru traffic and hospital administrators to lie about their tests gathered, and are feeding artificial data to the wastewater monitoring system. But that strikes me as exceptionally unlikely, the kind of conspiracy that would get exposed in 0.2 seconds flat by somebody somewhere with eyeballs and a brain.

In other words I think this good news is real. That doesnt mean were out of the woods. Were still experiencing high case numbers, so it isnt time to go to birthday parties and hug everyone you see again. But were trending in a positive direction.

Whats next in the world of testing?

The last time I wrote about testing, I looked at ways to make it easier for everyone involved. And most of those recommendations have been adopted. Were doing widespread sewage testing. Many test sites now get a saliva sample, and some just swab the shallow part of your nostril, not the part deep inside your skull. And many but not all businesses have incentivized their employees to stay home if theyre sick. Thats good!

I think we can still do better, though. In particular, I think we need to put more emphasis on rapid testing, an evolving field that has the potential to cut transmission of the disease to near-zero.

Our current testing setup doesnt do much to prevent the virus spread. People are most contagious in the day or two before and the day or two after they first exhibit symptoms, so testing them once they show symptoms and then giving them the results a couple days later doesnt mitigate the peak of the spread. Ideally, wed want to test even healthy people, especially in high-risk or high-importance areas.

The good news: we now have tests that can respond within minutes. These are antigen tests that are described as a lab on a swab. Essentially, you get a nasal swab or saliva sample, mix it with a buffer liquid, and then drop it on one end of a test strip. Capillary action the same force that causes your whole paper towel to get wet even if you only expose one corner to water drags the solution across the strip.

At the other end of the strip lay coronavirus antibodies. If the virus is present, the antibodies bind to the virus, just as they would inside of your body. And that binding triggers a marker that changes color. Essentially, it works almost like a pregnancy test: if you see the strip light up, you have coronavirus.

Now, this process takes minutes and is really easy to administer: sample, mix it, drop it on a test strip. These tests can cost about $1 or $2 each, where the PCR tests described earlier usually cost about $100.

Theyre also way less accurate.

Remember how PCR turns one coronavirus copy into millions or billions, making it easy to spot? The antigen tests dont do that, so theyre relying on some amount of chance to make sure the virus interacts with the antibodies on the strip. Antigen tests have a success rate of 50% to 90%. PCR, when done right, is about 98%. These rapid tests are going to tell a lot of people who really do have the disease that they dont, and that causes problems, to be sure.

But that downside is mitigated by how quick and cheap they are. Lets say you own a business that wants to test people every day, and your test has an 80% success rate. If each test is independent (and early indications say thats largely the case), the odds that someone with the coronavirus will test positive at least once after two tests is 96%. After three tests, its 99.2%. As Bettina Fries, chief of infectious diseases at Stony Brook University, told Science magazine, Even if the sensitivity [of antigen tests] is not perfect, if you test over and over you will pick up those cases.

Remember, this test will catch positives before symptoms occur, so even with three days of tests, youre likely going to get a result more quickly than someone waiting for their cough to get bad and drive to a testing facility, then wait for the PCR test to be processed and the results to be reported back.

There are plenty of situations in which youd want the higher accuracy of the PCR tests. But its also easy to imagine cases in which youd want the fast, cheap test. For the general public, catching 50% to 90% of coronavirus cases early would decimate the effective transmission rate, or Rt, and drive our case numbers way down. We need to let go of the notion that all the tests have to be perfect, Fries said.

Perfect can be the enemy of the good, and good repeated over time is enough to decimate the virus. Rapid tests are good.

Andy Larsen is a Salt Lake Tribune sports reporter who covers the Utah Jazz. During this crisis, he has been assigned to dig into the numbers surrounding the coronavirus. You can reach Andy at alarsen@sltrib.com or on Twitter at @andyblarsen.

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Coronavirus testing: How it works, why Utah's tests are down, and what's coming next? - Salt Lake Tribune

If you want to speed up the flow of outdoor air into a room, you could also take a box fan, place it in a window and blast it outward, Dr. Jimenez said. When any amount of air leaves, that same amount of air returns its a fixed volume. Therefore, the fan should help pull in the same amount of outdoor air.

If you have air-conditioning in your home, no one is saying that you need to give up on it entirely. When its sweltering out, air-conditioning can be essential not only to help you function but also to avoid heatstroke.

But if you are going to spend time in a cooled space with other people, it may be worth understanding a bit more about the cool air you are breathing. Basically, all air-conditioning falls into one of three categories.

The unit cools both indoor and outdoor air.

The unit cools and recirculates only indoor air.

The unit relies entirely on pulling in outdoor air. (These are uncommon outside hospitals and labs.)

Centralized-air systems, such as those common in office buildings, dorms and some large apartment buildings, often fall in category one. Dr. Jimenez and other building scientists involved in coronavirus prevention are currently advising owners of businesses and buildings with category one systems to adjust the ratio to pull in more outdoor air, an enterprise that can be costly. Take a casino in Las Vegas, which is kept cool enough to keep people gambling inside while its 120 degrees Fahrenheit outside. Cooling that hot outdoor air will be more expensive than recirculating the already cool inside air. But given that keeping customers healthy is also a priority, more are willing to revisit their approach, Dr. Jimenez said.

Few of us have the ability to adjust our air-conditioning in this way. Most window units sitting with their rears facing the outdoors, for example, fall into category two. Instead of pulling in outdoor air, they are dumping heat from the room outdoors, said William Bahnfleth, a professor of architectural engineering at Penn States Institutes of Energy and the Environment.

If you live alone, or with people youre sure arent infectious, those units are fine. But if you give in to throwing that birthday dinner for your parents, or if your teenager has been less than strict about staying home, its worth remembering that any virus thats present will be mixed in to the recirculating indoor air, Dr. Jimenez said.

And so, if you have to have people over, it may be preferable to revert to rule one: When in doubt, open the windows. Or better yet, go outside.

So what do you do if youre stuck with a unit that primarily recirculates indoor air and its unrealistic to open the window? This is where filters come in. The right filter is just as effective as pulling in outside air, said Dr. Edward A. Nardell, a professor at Harvard Medical School who has written about the role that air-conditioning plays in spreading airborne diseases.

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Your Hot-Weather Guide to Coronavirus, Air-Conditioning and Airflow - The New York Times

San Francisco's coronavirus response has been far from perfect.

But with just over 7,000 cases and 64 deaths, in a population of over 800,000, it's better off than most U.S. cities, experts say.

At this stage, the city remains on the state's watchlist although things have recently been frozenfor the past few days because of a data glitch and schools will open later this month with 100% remote learning.

But hospitals were never overwhelmed. That allowed the University of California, San Francisco to send medical volunteers to other parts of the country that have been harder hit by the virus.

The city's health experts say that there are lessons to be drawn from San Francisco's response. Dr. Bob Wachter, chairman of the department of medicine at UC San Francisco, has recently highlighted in a series of tweet storms how the city has one of the lowest rates of cases per 100,000, compared to other large U.S. cities. The first months of the response in March and April were particularly impressive, he notes, although things took a turn for the worse in the early summer months.

Wachter created the following chart, which shows that as of July 31, San Francisco had the third-lowest case rate and lowest death rate of the 20 largest cities.

In an interview, he shared some of the major factors that might explain why case counts remain relatively low compared to other parts of the country and state. Overall, California has seen more than 540,000 cases and more than 10,000 deaths.

A pedestrian wearing a protective mask walks past signage at the Google San Francisco office in San Francisco, California, on Monday, July 27, 2020.

David Paul Morris | Bloomberg | Getty Images

Many of the city's largest companies took an early leap in recommending that their workers remain at home, rather than commuting into the office. Of course, it's worth noting that many of these companies are in the business of software, so remote work is a far easier proposition. Twitter, Google, and other techcompanies with big offices in San Francisco all asked employees to stay home back in early March.

"Corporate leaders in the Bay Area were early to recognizing that this was going to be a big deal," said Dr. Wachter. "I remember it hitting me how serious it was when Google told everyone to stay home, and I figured they must know something."

A person wearing a protective mask receives hand sanitizer while attending mass outside the National Shrine of St. Francis of Assisi Catholic Church in San Francisco, California, on Tuesday, July 14, 2020.

David Paul Morris | Bloomberg | Getty Images

California is one of the states that requires people to wear masks. Moreover,polls and surveys have consistently found that Californians are actually following the rule more than residents of most other states.

The one exception to the rule, in San Francisco at least, seems to be the parkswhere city officials have drawn circles in chalk to establish social distancing. But for the most part, people do wear masks while on walks and in grocery stores. City health officials have also been consistent in recommending masks and cloth coverings.

"There's also social pressure here in San Francisco," explained Wachter. "In San Francisco, if you go to a gathering with one person having a mask off, it's likely that person would be looked at funny and their friends might even say something."

San Francisco Mayor London Breed

Justin Sullivan | Getty Images

It hasn't been easy to be a health official in America since the outset of the pandemic. In the Bay Area, public health experts have reported harassmentfrom residents that took issue with the guidelines.

But they still took early stands based on science and stuck to them consistently.

San Francisco Mayor London Breed declared a state of emergency in late February, before the city had confirmed a single case of the coronavirus. She was also very early to ban gatherings of more than 1,000 people.

"In retrospect, it was gutsy as hell," said Wachter. "Our local politicians have demonstrated they have the courage to do it, and the city's citizens have demonstrated in return that they will take the time to understand what's going on and they'll accept it."

In mid-July San Francisco Health Director Dr. Grant Colfax issued some concerning predictions about where the city could be going. He recently estimated a worst case scenario where the city could seea peak of 6,000 patients hospitalized by early to mid-October.

Wachter feels cautiously optimistic but recognizes that it's hard to know what the future may hold. People are getting fatigued by the shutdowns and may be looking for reasons to avoid the public health guidelines. But he also says some of the recent small surges were to be expected as the city starts to allow some stores to reopen and restaurants to serve customers outdoors.

"You can't be on strict lockdown for two years so we must accept some cases, but we're ready for it," he said.

He also notes that hospitals have had a bit of time to prepare, so it's better to see a modest uptick now than in March. Back then, there were widespread shortages of personal protective equipment for health care workers.

Overall, he feels relatively confident that San Francisco residents will continue to do the right thing. Despite mounting pandemic fatigue, there's still widespread acceptance of wearing masks and in social distancing compared to other parts of the country.

"From what I've seen so far, I expect that we'll be able to manage alright and get things under control," he said.

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How San Francisco succeeded more than other U.S. cities in fighting the coronavirus - CNBC