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Tag: infectious-disease epidemiologist

  • No One Really Knows How Much COVID Is Silently Spreading … Again

    No One Really Knows How Much COVID Is Silently Spreading … Again

    In the early days of the pandemic, one of the scariest and most surprising features of SARS-CoV-2 was its stealth. Initially assumed to transmit only from people who were actively sick—as its predecessor SARS-CoV did—the new coronavirus turned out to be a silent spreader, also spewing from the airways of people who were feeling just fine. After months of insisting that only the symptomatic had to mask, test, and isolate, officials scrambled to retool their guidance; singing, talking, laughing, even breathing in tight quarters were abruptly categorized as threats.

    Three years later, the coronavirus is still silently spreading—but the fear of its covertness again seems gone. Enthusiasm for masking and testing has plummeted; isolation recommendations have been pared down, and may soon entirely disappear. “We’re just not communicating about asymptomatic transmission anymore,” says Saskia Popescu, an infectious-disease epidemiologist and infection-prevention expert at George Mason University. “People think, What’s the point? I feel fine.”

    Although the concern over asymptomatic spread has dissipated, the threat itself has not. And even as our worries over the virus continue to shrink and be shunted aside, the virus—and the way it moves between us—is continuing to change. Which means that our best ideas for stopping its spread aren’t just getting forgotten; they’re going obsolete.

    Read: A negative COVID test has never been so meaningless

    When SARS-CoV-2 was new to the world and hardly anyone had immunity, symptomless spread probably accounted for most of the virus’s spread—at least 50 percent or so, says Meagan Fitzpatrick, an infectious-disease transmission modeler at the University of Maryland’s School of Medicine. People wouldn’t start feeling sick until four, five, or six days, on average, after being infected. In the interim, the virus would be xeroxing itself at high speed in their airway, reaching potentially infectious levels a day or two before symptoms started. Silently infected people weren’t sneezing and coughing—symptoms that propel the virus more forcefully outward, increasing transmission efficiency. But at a time when tests were still scarce and slow to deliver results, not knowing they had the virus made them dangerous all the same. Precautionary tests were still scarce, or very slow to deliver results. So symptomless transmission became a norm, as did epic superspreading events.

    Now, though, tests are more abundant, presymptomatic spread is a better-known danger, and repeated rounds of vaccination and infection have left behind layers of immunity. That protection, in particular, has slashed the severity and duration of acute symptoms, lowering the risk that people will end up in hospitals or morgues; it may even be chipping away at long COVID. At the same time, though, the addition of immunity has made the dynamics of symptomless transmission much more complex.

    On an individual basis, at least, silent spread could be happening less often than it did before. One possible reason is that symptoms are now igniting sooner in people’s bodies, just three or so days, on average, after infection—a shift that roughly coincided with the rise of the first Omicron variant and could be a quirk of the virus itself. But Aubree Gordon, an infectious-disease epidemiologist at the University of Michigan, told me that faster-arriving sicknesses are probably being driven in part by speedier immune responses, primed by past exposures. That means that illness might now coincide with or even precede the peak of contagiousness, shortening the average period in which people spread the virus before they feel sick. In that one very specific sense, COVID could now be a touch more flulike. Presymptomatic transmission of the flu does seem to happen on occasion, says Seema Lakdawala, a virologist at Emory University. But in general, “people tend not to hit their highest viral levels until after they develop symptoms,” Gordon told me.

    Coupled with more population-level immunity, this arrangement could be working in our favor. People might be less likely to pass the virus unwittingly to others. And thanks to the defenses we’ve collectively built up, the pathogen itself is also having more trouble exiting infected bodies and infiltrating new ones. That’s almost certainly part of the reason that this winter hasn’t been quite as bad as past ones have, COVID-wise, says Maia Majumder, an infectious-disease modeler at Harvard Medical School and Boston Children’s Hospital.

    That said, a lot of people are still undoubtedly catching the coronavirus from people who aren’t feeling sick. Infection per infection, the risk of superspreading events might now be lower, but at the same time people have gotten chiller about socializing without masks and testing before gathering in groups—a behavioral change that’s bound to counteract at least some of the forward shift in symptoms. Presymptomatic spread might be less likely nowadays, but it’s nowhere near gone. Multiply a small amount of presymptomatic spread by a large number of cases, and that can still seed … another large number of cases.

    Read: You probably have an asymptomatic infection right now

    There could be some newcomers to the pool of silent spreaders, too—those who are now transmitting the virus without ever developing symptoms at all. With people’s defenses higher than they were even a year and a half ago, infections that might have once been severe are now moderate or mild; ones that might have once been mild are now unnoticeable, says Seyed Moghadas, a computational epidemiologist at York University. At the same time, though, immunity has probably transformed some symptomless-yet-contagious infections into non-transmissible cases, or kept some people from getting infected at all. Milder cases are of course welcome, Fitzpatrick told me, but no one knows exactly what these changes add up to: Depending on the rate and degree of each of those shifts, totally asymptomatic transmission might now be more common, less common, or sort of a wash.

    Better studies on transmission patterns would help cut through the muck; they’re just not really happening anymore. “To get this data, you need to have pretty good testing for surveillance purposes, and that basically has stopped,” says Yonatan Grad, an infectious-disease epidemiologist at Harvard’s School of Public Health.

    Meanwhile, people are just straight-up testing less, and rarely reporting any of the results they get at home. For many months now, even some people who are testing have been seeing strings of negative results days into bona-fide cases of COVID—sometimes a week or more past when their symptoms start. That’s troubling on two counts: First, some legit COVID cases are probably getting missed, and keeping people from accessing test-dependent treatments such as Paxlovid. Second, the disparity muddles the start and end of isolation. Per CDC guidelines, people who don’t test positive until a few days into their illness should still count their first day of symptoms as Day 0 of isolation. But if symptoms might sometimes outpace contagiousness, “I think those positive tests should restart the isolation clock,” Popescu told me, or risk releasing people back into society too soon.

    Read: People are fed up with rapid tests

    American testing guidelines, however, haven’t undergone a major overhaul in more than a year—right after Omicron blew across the nation, says Jessica Malaty Rivera, an infectious-disease epidemiologist at Boston Children’s Hospital. And even if the rules were to undergo a revamp, they wouldn’t necessarily guarantee more or better testing, which requires access and will. Testing programs have been winding down for many months; free diagnostics are once again growing scarce.

    Through all of this, scientists and nonscientists alike are still wrestling with how to define silent infection in the first place. What counts as symptomless depends not just on biology, but behavior—and our vigilance. As worries over transmission continue to falter and fade, even mild infections may be mistaken for quiet ones, Grad told me, brushed off as allergies or stress. Biologically, the virus and the disease may not need to become that much more muted to spread with ease: Forgetting about silent spread may grease the wheels all on its own.

    Katherine J. Wu

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  • Norovirus Is Almost Impossible to Stop

    Norovirus Is Almost Impossible to Stop

    In one very specific and mostly benign way, it’s starting to feel a lot like the spring of 2020: Disinfection is back.

    “Bleach is my friend right now,” says Annette Cameron, a pediatrician at Yale School of Medicine, who spent the first half of this week spraying and sloshing the potent chemical all over her home. It’s one of the few tools she has to combat norovirus, the nasty gut pathogen that her 15-year-old son was recently shedding in gobs.

    Right now, hordes of people in the Northern Hemisphere are in a similarly crummy situation. In recent weeks, norovirus has seeded outbreaks in several countries, including the United Kingdom, Canada, and the United States. Last week, the U.K. Health Security Agency announced that laboratory reports of the virus had risen to levels 66 percent higher than what’s typical this time of year. Especially hard-hit are Brits 65 and older, who are falling ill at rates that “haven’t been seen in over a decade.”

    Americans could be heading into a rough stretch themselves, Caitlin Rivers, an infectious-disease epidemiologist at Johns Hopkins University, told me, given how closely the U.S.’s epidemiological patterns tend to follow those of the U.K. “It does seem like there’s a burst of activity right now,” says Nihal Altan-Bonnet, a norovirus researcher at the National Institutes of Health. At her own practice, Cameron has been seeing the number of vomiting and diarrhea cases among her patients steadily tick up. (Other pathogens can cause gastrointestinal symptoms as well, but norovirus is the most common cause of foodborne illness in the United States.)

    To be clear, this is more a nauseating nuisance than a public-health crisis. In most people, norovirus triggers, at most, a few miserable days of GI distress that can include vomiting, diarrhea, and fevers, then resolves on its own; the keys are to stay hydrated and avoid spreading it to anyone vulnerable—little kids, older adults, the immunocompromised. The U.S. logs fewer than 1,000 annual deaths out of millions of documented cases. In other high-income countries, too, severe outcomes are very rare, though the virus is far more deadly in parts of the world with limited access to sanitation and potable water.

    Still, fighting norovirus isn’t easy, as plenty of parents can attest. The pathogen, which prompts the body to expel infectious material from both ends of the digestive tract, is seriously gross and frustratingly hardy. Even the old COVID standby, a spritz of hand sanitizer, doesn’t work against it—the virus is encased in a tough protein shell that makes it insensitive to alcohol. Some have estimated that ingesting as few as 18 infectious units of virus can be enough to sicken someone, “and normally, what’s getting shed is in the billions,” says Megan Baldridge, a virologist and immunologist at Washington University in St. Louis. At an extreme, a single gram of feces—roughly the heft of a jelly bean—could contain as many as 5.5 billion infectious doses, enough to send the entire population of Eurasia sprinting for the toilet.

    Unlike flu and RSV, two other pathogens that have bounced back to prominence in recent months, norovirus mainly targets the gut, and spreads especially well when people swallow viral particles that have been released in someone else’s vomit or stool. (Despite its “stomach flu” nickname, norovirus is not a flu virus.) But direct contact with those substances, or the food or water they contaminate, may not even be necessary: Sometimes people vomit with such force that the virus gets aerosolized; toilets, especially lidless ones, can send out plumes of infection like an Air Wick from hell. And Altan-Bonnet’s team has found that saliva may be an unappreciated reservoir for norovirus, at least in laboratory animals. If the spittle finding holds for humans, then talking, singing, and laughing in close proximity could be risky too.

    Read: Whatever happened to toilet plumes?

    Once emitted into the environment, norovirus particles can persist on surfaces for days—making frequent hand-washing and surface disinfection key measures to prevent spread, says Ibukun Kalu, a pediatric infectious-disease specialist at Duke University. Handshakes and shared meals tend to get dicey during outbreaks, along with frequently touched items such as utensils, door handles, and phones. One 2012 study pointed to a woven plastic grocery bag as the source of a small outbreak among a group of teenage soccer players; the bag had just been sitting in a bathroom used by one of the girls when she fell sick the night before.

    Once a norovirus transmission chain begins, it can be very difficult to break. The virus can spread before symptoms start, and then for more than a week after they resolve. To make matters worse, immunity to the virus tends to be short-lived, lasting just a few months even against a genetically identical strain, Baldridge told me.

    Day cares, cruise ships, schools, restaurants, military training camps, prisons, and long-term-care facilities can be common venues for norovirus spread. “I did research with the Navy, and it just goes through like wildfire,” often sickening more than half the people on tightly packed ships, says Robert Frenck, the director of the Vaccine Research Center at Cincinnati Children’s Hospital. Households, too, are highly susceptible to spread: Once the virus arrives, the entire family is almost sure to be infected. Baldridge, who has two young children, told me that her household has weathered at least four bouts of norovirus in the past several years.

    (A pause for some irony: In spite of norovirus’s infectiousness, scientists did not succeed in culturing it in labs until just a few years ago, after nearly half a century of research. When researchers design challenge trials to, say, test new vaccines, they still need to dose volunteers with norovirus that’s been extracted from patient stool, a gnarly practice that’s been around for more than 50 years.)

    Norovirus spread doesn’t have to be a foregone conclusion. Some people do get lucky: Roughly 20 percent of European populations, for instance, are genetically resistant to common norovirus strains. “So you can hope,” Frenck told me. For the rest of us, it comes down to hygiene. Altan-Bonnet recommends diligent hand-washing, plus masking to ward off droplet-borne virus. Sick people should isolate themselves if they can. “And keep your saliva to yourself,” she told me.

    Read: The stomach-flu mystery

    Rivers and Cameron have both managed to halt the virus in their homes in the past; Cameron may have pulled it off again this week. The family fastidiously scrubbed their hands with hot water and soap, donned disposable gloves when touching shared surfaces, and took advantage of the virus’s susceptibility to harsh chemicals and heat. When her son threw up on the floor, Cameron sprayed it down with bleach; when he vomited on his quilt, she blasted it twice in the washing machine on the sanitizing setting, then put it through the dryer at a super high temp. Now a couple of days out from the end of their son’s sickness, Cameron and her husband appear to have escaped unscathed.

    Norovirus isn’t new, and this won’t be the last time it hits. In a lot of ways, “this is back to basics,” says Samina Bhumbra, the medical director of infection prevention at Riley Children’s Hospital. After three years of COVID, the world has gotten used to thinking about infections in terms of airways. “We need to recalibrate,” Bhumbra told me, “and remember that other things exist.”

    Katherine J. Wu

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  • The Future of Monkeypox

    The Future of Monkeypox

    The World Health Organization has recommended a new name for monkeypox, asking countries to forget the original term in favor of a new one, “mpox,” that scientists hope will help destigmatize the disease. But in the United States, the request seems to be arriving late. The outbreak here has already been in slow retreat for months—and has already left many Americans’ minds.

    About 15 cases are now being recorded among Americans each day, less than 4 percent of the tally when the surge was at its worst. After a sluggish and bungled early rollout, tests and treatments for the virus are more available; more than a million doses of the two-shot Jynneos smallpox vaccine have found their way into arms. San Francisco and New York—two of the nation’s first cities to declare mpox a public-health emergency this past summer—have since allowed those orders to expire; so have the states of New York and Illinois. “I think this is the endgame,” says Caitlin Rivers, an infectious-disease epidemiologist at the Johns Hopkins Center for Health Security.

    But “endgame” doesn’t mean “over”—and mpox will be with us for the foreseeable future. The U.S. outbreak is only now showing us its long and ugly tail: 15 daily cases is not zero daily cases; even as the number of new infections declines, inequities are growing. Black and Latino people make up a majority of new mpox cases and are contracting the disease at three to five times the rate of white Americans, but they have received proportionately fewer vaccines. “Now it’s truly the folks who are the most marginalized that we’re seeing,” says Ofole Mgbako, a physician and population-health researcher at New York University. “Which is also why, of course, it’s fallen out of the news.” If the virus sticks around (as it very likely could), and if the disparities persist (as they almost certainly will), then mpox could end up saddling thousands of vulnerable Americans each year with yet another debilitating, stigmatized, and neglected disease.

    Read: America should have been able to handle monkeypox

    At this point, there’s not even any guarantee that this case downturn will persist. “I’m not convinced that we’re out of the woods,” says Sara Bares, an infectious-disease physician at the University of Nebraska Medical Center, in Omaha. Immunity, acquired through infection or vaccines, is now concentrated among those at highest risk, says Jay Varma, a physician and epidemiologist at Weill Cornell Medicine. But researchers still don’t know how well those defenses can stave off another infection, or how long they might last—gaps in knowledge that may be tough to fill, now that incidence is so low. And although months of advocacy and outreach from the LGBTQ community have cut down on risky sexual activities, many cautionary trends will eventually reset to their pre-outbreak norm. “We know extensively from other sexually transmissible infections that behavior change is not usually the most sustained response,” says Boghuma Kabisen Titanji, an infectious-disease physician at Emory University.

    At the same time, this year’s mpox outbreaks are stranger and more unwieldy than those that came before. A ballooning body of evidence suggests that people can become infectious before they develop symptoms, contrary to prior understanding; some physicians are concerned that patients, especially those who are immunocompromised, might remain infectious after the brunt of visible illness resolves, says Philip Ponce, an infectious-disease physician at the University of Texas Health Science Center at San Antonio and the medical director of San Antonio’s Kind Clinic. (Some 40 percent of Americans who have been diagnosed with mpox are living with HIV.) Researchers still don’t have a good grip on which bodily fluids and types of contact may be riskiest over the trajectory of a sickness. Cases are still being missed by primary-care providers who remain unfamiliar with the ins and outs of diagnosis and testing, especially in people with darker skin. And although this epidemic has, for the most part, continued to affect men who have sex with men, women and nonbinary people are getting sick as well, to an underappreciated degree.

    Read: What should worry most Americans about our monkeypox response

    Intel on the only mpox-fighting antiviral on the shelf, a smallpox drug called tecovirimat, also remains concerningly scant, even as experts worry that the virus could develop resistance. The treatment has been given a conditional greenlight for use in people who are currently, or at risk of becoming, severely sick. Anecdotally, it seems to work wonders, shaving days or weeks off the painful, debilitating course of symptoms that can send infected people into long-term isolation. But experts still lack rigorous data in humans to confirm just how well it works, Bares, who’s among the scientists involved in a nationwide study of the antiviral, told me. And although clinical trials for tecovirimat are under way, she added, in the U.S., they’re “struggling to enroll patients” now that infections have plummeted to such a sustained low. It’s a numerical problem as well as a sociocultural one. “The urgency with which people answer questions declines as case counts go down,” Varma told me.

    Recent CDC reports show that a growing proportion of new infections aren’t being reported with a known sexual-contact history, stymieing efforts at contact tracing. That might in part be a product of the outbreak’s gradual migration from liberal, well-off urban centers, hit early on in the epidemic, to more communities in the South and Southwest. “In small towns, the risk of disclosure is high,” Bares told me. In seeking care or vaccination, “you’re outing yourself.” When mpox cases in Nebraska took an unexpected nosedive earlier this fall, “a colleague and I asked one another, ‘Do you think patients are afraid to come in?’” Those concerns can be especially high in certain communities of color, Ponce told me. San Antonio’s Latino population, for instance, “tends to be much more conservative; there’s much more stigma associated with one being LGBT at all, let alone being LGBT and trying to access biomedical interventions.”

    Hidden infections can become fast-spreading ones. Monitoring an infectious disease is far easier when the people most at risk have insurance coverage and access to savvy clinicians, and when they are inclined to trust public-health institutions. “That’s predominantly white people,” says Ace Robinson, the CEO of the Pierce County AIDS Foundation, in Washington. Now that the mpox outbreak is moving out of that population into less privileged ones, Robinson fears “a massive undercount” of cases.

    Americans who are catching the virus during the outbreak’s denouement are paying a price. The means to fight mpox are likely to dwindle, even as the virus entrenches itself in the population most in need of those tools. One concern remains the country’s vaccination strategy, which underwent a mid-outbreak shift: To address limited shot supply, the FDA authorized a new dosing method with limited evidence behind it—a decision that primarily affected people near the back of the inoculation line. The method is safe but tricky to administer, and it can have tough side effects: Some of Titanji’s patients have experienced swelling near their injection site that lasted for weeks after their first dose, and now “they just don’t want to get another shot.”

    The continued shift of mpox into minority populations, Robinson told me, is also further sapping public attention: “As long as this is centered in BIPOC communities, there’s going to be less of a push.” Public interest in this crisis was modest even at its highest point, says Steven Klemow, an infectious-disease physician at Methodist Dallas Medical Center and the medical director of Dallas’s Kind Clinic. Now experts are watching that cycle of neglect reinforce itself as the outbreak continues to affect and compress into marginalized communities, including those that have for decades borne a disproportionate share of the burden of sexually associated infections such as syphilis, gonorrhea, and HIV. “These are not the groups that necessarily get people jumping on their feet,” Titanji told me.

    Some of the people most at risk are moving on as well, Robinson told me. In his community in Washington, he was disappointed to see high rates of vaccine refusal at two recent outreach events serving the region’s Black and American Indian populations. “They had no knowledge of the virus,” he told me. Titanji has seen similar trends in her community in Georgia. “There’s some sense of complacency, like, ‘It’s no longer an issue, so why do I need to get vaccinated?’” she said.

    Read: America is zooming through the pandemic panic-neglect cycle

    The tide seems unlikely to shift. Even tens of thousands of cases deep into the American outbreak, sexual-health clinics—which have been on the front lines of the mpox response—remain short on funds and staff. Although the influx of cases has slowed, Ponce and Klemow are still treating multiple mpox patients a week while trying to keep up the services they typically offer—at a time when STI rates are on a years-long rise. “We’re really assuming that this is going to become another sexually associated disease that is going to be a part of our wheelhouse that we’ll have to manage for the indefinite future,” Klemow told me. “We’ve had to pull resources away from our other services that we provide.” The problem could yet worsen if the national emergency declared in August is allowed to expire, which would likely curb the availability of antivirals and vaccines.

    Rivers still holds out hope for eliminating mpox in the U.S. But getting from low to zero isn’t as easy as it might seem. This current stretch of decline could unspool for years, even decades, especially if the virus finds a new animal host. “We’ve seen this story play out so many times before,” Varma told me. Efforts to eliminate syphilis from the U.S. in the late ’90s and early 2000s, for instance, gained traction for a while—then petered out during what could have been their final stretch. It’s the classic boom-bust cycle to which the country is so prone: As case rates fall, so does interest in pushing them further down.

    Our memories of public-health crises never seem to linger for long. At the start of this mpox outbreak, Titanji told me, there was an opportunity to shore up our systems and buffer ourselves against future epidemics, both imported and homegrown. The country squandered it and failed to send aid abroad. If another surge of mpox cases arrives, as it very likely could, she said, “we will again be going back to the drawing board.”

    Katherine J. Wu

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