Why Some People Are Still Getting Sick – but Not With COVID

 In COVID-19

On September 18 Orianna Carvalho woke up at 3 A.M. with a sore throat and the snif­fles. At first, she thought her symp­toms were caused by aller­gies. But as the min­utes ticked by, she began to worry they were caused by COVID-19. The fol­low­ing morn­ing, Carvalho got tested at the University of Rhode Island, where she is a first-year doc­tor­al stu­dent. Over the next few hours she devel­oped a fever, and the cat­a­stro­phiz­ing began in earnest. When Carvalho final­ly learned that the cause of her misery was not COVID but the common cold, she was relieved but also sur­prised. “I have been so care­ful — wear­ing a mask every time I go some­where, keep­ing at least six feet away from other people, using hand san­i­tiz­er and wash­ing my hands,” she says. “I don’t know how I got sick.”

Carvalho is not alone. Many Americans have been puz­zled to find that their best efforts to avoid COVID-19 have not always pro­tect­ed them from less trou­bling infec­tions such as colds, stom­ach bugs and strep throat. How have other pathogens slipped through our anti-COVID defens­es? There are no clear-cut answers, but the work of infec­tious dis­ease spe­cial­ists, virol­o­gists and epi­demi­ol­o­gists — much of it con­duct­ed decades before the cur­rent pan­dem­ic — pro­vides some clues. Their research shows that many microbes are more numer­ous, hardy and con­ta­gious than SARS-CoV‑2, the virus that causes COVID-19. And for many of us, even our best efforts are not good enough.

The public health mea­sures taken to stem the spread of SARS-CoV‑2, which has been respon­si­ble for the deaths of more than 207,000 people in the U.S. to date, have also affect­ed the preva­lence of other res­pi­ra­to­ry virus­es. This year the Southern Hemisphere essentially skipped flu season, which typ­i­cal­ly hits coun­tries such as Australia, Chile and South Africa in May or June. Data from Australia sug­gest that although pan­dem­ic restric­tions pushed many non-flu virus­es out of cir­cu­la­tion, a group of cold-caus­ing pathogens known as rhi­novirus­es stuck around. A sim­i­lar trend could be in store for the U.S., accord­ing to researchers who are track­ing trans­mis­sion of res­pi­ra­to­ry virus­es in New York State, Washington State and Texas. Pedro Piedra, a pedi­atric infec­tious dis­ease spe­cial­ist at Baylor College of Medicine, says that although he has seen a sig­nif­i­cant decrease in many common res­pi­ra­to­ry virus­es during the pan­dem­ic, he has noticed an uptick in rhi­novirus­es this fall.

Some virol­o­gists believe that the sheer number of virus­es that cause the common cold can make it exceed­ing­ly dif­fi­cult to avoid catch­ing one: there are around 200 dif­fer­ent pathogens. These include four coro­n­avirus­es (the group that includes SARS-CoV‑2); four parain­fluen­za virus­es (which, despite their name, bear no rela­tion to influen­za virus­es); res­pi­ra­to­ry syn­cy­tial virus; and 160 dif­fer­ent rhi­novirus­es. Viral cen­sus­es have revealed that dozens of these rhinoviruses cir­cu­late in any one place at a given time. “You might be immune to the flu, but you are not going to be immune to all those rhi­novirus­es,” says James Gern, a rhi­novirus researcher at the University of Wisconsin – Madison. “That’s one unique fea­ture of rhi­novirus­es — you are always going to be sus­cep­ti­ble to some.”

But there is only one SARS-CoV‑2 virus, and it has proved to be more than enough to wreak havoc on our lives. The per­sis­tence of rhi­novirus­es during the pan­dem­ic may be the result of not only their impres­sive number but also their prim­i­tive nature, says Ian Mackay, a virol­o­gist at the University of Queensland in Australia. Similar to the flu virus, SARS-CoV‑2 is a more highly evolved virus that is enclosed in a fatty “lipid” mem­brane. This enve­lope can cloak the pathogen from anti­bod­ies deployed by the human immune system, enabling it to infect cells unde­tect­ed. But it can also break down after expo­sure to the envi­ron­ment or a good hand­wash­ing, ren­der­ing the virus harm­less. Rhinoviruses, on the other hand, never evolved an enve­lope. These so-called naked virus­es, which also include the gut-dis­tress-induc­ing norovirus­es, are more resis­tant to san­i­tiz­ers and dis­in­fec­tants and may last longer on fingertips and surfaces.

Although it is pos­si­ble to pick up res­pi­ra­to­ry virus­es from con­t­a­m­i­nat­ed sur­faces, most experts say we are more likely to get sick through con­tact with infect­ed people. In 1969 half of a group of men win­ter­ing at a remote Antarctic base devel­oped signs and symptoms of the common cold after being iso­lat­ed for 17 weeks. Scientists never iden­ti­fied the source of the out­break, but Mackay and others think it is pos­si­ble that the men enter­ing the base might not have been as healthy as they looked. Asymptomatic spread has gotten a lot of atten­tion during the COVID-19 pan­dem­ic: stud­ies sug­gest 40 to 45 per­cent of SARS-CoV‑2 trans­mis­sion comes from people not yet showing symptoms. Many colds and flus may also be passed along by people who do not have symp­toms, although to what extent this spread occurs is an open ques­tion. At least one study detect­ed rhinoviruses in a third of asymptomatic children.

“Children, in par­tic­u­lar, are a petri dish for trans­mis­sion,” says >Arnold Monto, an epi­demi­ol­o­gist at the University of Michigan, who stud­ies the spread of respiratory illnesses within house­holds. Because kids are prone to eye rub­bing and nose pick­ing, they can quick­ly con­t­a­m­i­nate their home with a menagerie of virus­es and bac­te­ria. Unlike the acute res­pi­ra­to­ry infec­tions that typ­i­cal­ly come and go in a matter of weeks, chil­dren can harbor chronic infections with bac­te­ria — such as Streptococcus pyo­genes, which causes strep throat — for months before ever making them­selves or others sick. Tara Smith, an epi­demi­ol­o­gist at Kent State University, says it is unclear how such bac­te­ria move from harm­less col­o­niz­er to inva­sive pathogen, but the stress of the pan­dem­ic could play a role. And kids are not the only germ fac­to­ries in our homes: pets are common car­ri­ers of many pathogens. “People prob­a­bly get sick from their ani­mals more than we real­ize,” Smith says.

Despite the myriad pos­si­bil­i­ties, many experts believe the expla­na­tion for why some of us are still get­ting rou­tine infec­tions is fairly mun­dane. “Some people may think they are better pro­tect­ed than they actu­al­ly are,” Smith says. Gern agrees: “If cold virus­es are still spread­ing, that means we are still having person-to-person con­tact,” he says. We live in a world where once ben­e­fi­cial actions — such as hug­ging a friend or going to the gym — now pose height­ened risks to our health. For her part, Carvalho thought she was doing every­thing she could to be safe. After months of stay­ing home, she returned to the gym for some social­ly dis­tanced mar­tial arts. She now sus­pects that it is how she got sick.

Since the begin­ning of the pan­dem­ic, more than 80,000 people who won­dered if they had a COVID infec­tion have called the telemed­i­cine com­pa­ny Doctor on Demand, accord­ing to Prentiss Taylor, a physi­cian and the company’s vice pres­i­dent of med­ical affairs. More than half of those cases were not referred for COVID-19 test­ing because some other res­pi­ra­to­ry afflic­tion was deemed more likely. Under the cir­cum­stances, catch­ing a cold instead of COVID might feel like dodg­ing a bullet. But the fact that other virus­es have been able to slip through our defens­es could serve as a warn­ing for future pan­demics, Mackay says. “If we ever see a new rhi­novirus come along, we will have even more trou­ble con­tain­ing it than SARS-CoV‑2. A rhi­novirus pan­dem­ic would be a mas­sive threat that would spread like that,” he adds, snap­ping his fin­gers. “And there’s no guar­an­tee it would only cause common colds.”

Scientific American source|articles

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