The 2017-2018 flu season is in full swing, and it’s a tough one. The New York Times recently reported that the season is “moderately severe” and likely to get worse, due in part to the virulence of the dominant circulating strain and concerns about the effectiveness of this year’s vaccine. (According to the CDC, vaccines are typically about 40-60% effective against infections in the U.S.; in a bad year, when the virus used to make the vaccine and dominant virus circulating among the public don’t match up, effectiveness has dropped to as low as 10%.)
That said, doctors still recommend the flu shot to help avoid catching and spreading the virus. Additionally, you should take basic precautions like staying home if you don’t feel well, washing your hands frequently, and avoiding people who are sick. Unfortunately, that’s easier said than done, particularly in congested urban areas like New York City where you cross paths with hundreds of people just taking the subway. With NYC currently experiencing widespread flu rates, as well as high reports of colds and other respiratory infections, one might start to feel like getting sick is inevitable.
The truth is, there has been little research into how respiratory viruses are distributed and transmitted in cities, and it may be even harder to avoid infected people than previously thought. According to a multi-arm study underway at Columbia University, 7-10% of New Yorkers out in public may be carrying a range of respiratory infections – and some may not even know it. The researchers are now trying to understand whether these carriers are able to spread the viruses to others.
Tracking Infections
When estimating the prevalence of viruses, the CDC relies on data from healthcare providers and laboratories, which report statistics for patients who have sought medical care for their symptoms. Among other things, this helps to create a geographic map of infections, identify which strains are circulating, and discover how strains are changing. But for cold and flu viruses that are so common, and so heavily surveilled, there are a lot of things we still don’t know about them. Why do some people get sick when others don’t? Why do symptoms vary from person to person? And how does the flu spread in the first place?
This new study could help answer these questions, in part by including data from a different group: people who are healthy enough to be walking around in Manhattan. Through one-time sampling at a major tourist attraction and several hospitals, as well as longer-term sampling at hospitals, schools, and daycares, the Virome of Manhattan project hopes to fill in gaps in the knowledge about how respiratory infections like the flu spread. Led by Jeffrey Shaman of the International Research Institute for Climate and Society and the Mailman School of Public Health, researchers are studying, among other things, what and where the infections are and the role people without symptoms might play in spreading them.
Asymptomatic Infections
Ruthie Birger is an Earth Institute postdoctoral fellow who performed the statistical analysis for the samples taken at the Manhattan tourist attraction. (No, we can’t tell you which one.) This portion of the study aims to provide a snapshot of respiratory infections in an average group of people walking around the city.
Researchers did two rounds of testing, one in summer 2016 and one in winter 2017. First, they conducted a survey to ascertain symptoms, demographics, and medical histories. Then, researchers administered nasopharyngeal swabs and ran a PCR panel, which detects common respiratory infections including rhinovirus (i.e. the “common cold”), coronavirus, and the flu.
In the nearly 3,000 samples taken, they found infection rates of 7.2% in the summer and about 10% in the winter. In the summer study, which was published in January, the most prevalent infection by far was rhinovirus/the common cold (71%), followed by coronavirus (21.5%). The remaining 7.4% included all other evaluated infections, including influenza (0.9%).
When taken with the results of symptom reporting, researchers believe this may be because people with more severe symptoms, especially fever, more often choose to stay home, and rhinovirus and coronavirus infections may more frequently produce mild or no symptoms. However, it could also mean that rhinovirus and coronavirus are more communicable, and/or able to avoid triggering an immune response in order to more easily grow or spread.
Though it’s good news that people with more serious illnesses like the flu may be heeding the advice of experts and staying home, the overall infection rate was higher than expected. It was particularly surprising how many people tested positive without reporting any symptoms. “The real take-home of the study is how many asymptomatic individuals there were,” says Birger. “Regardless of how we define ‘asymptomatic’, over 50% of individuals who tested positive were asymptomatic, with some definitions yielding over 90% asymptomatic.”
The researchers can’t be sure yet whether people without symptoms are contagious, in part because it is not currently known whether some of these infections are airborne or spread through other mechanisms, like droplet transmission. They hope the results will lend new insight into the range and severity of symptoms in people with respiratory infections, as well as how viruses might spread between people without symptoms. “We don’t really know the contribution of asymptomatic infections to transmission, but part of that is because it hasn’t been measured,” Birger explains. “Something like this is a first step: classifying what prevalence looks like.”
Future Research
When taken together with the rest of the ongoing study, researchers hope to get a clearer picture of how and why these infections spread. Improved estimates of asymptomatic infection rates can also help epidemiologists and health practitioners create better real-time disease monitoring and forecasting, which in turn could improve vaccine development, treatment strategies, and health outcomes.
Additionally, given how quickly mobile technology has advanced, as well as a growing interest in citizen science, Birger sees the potential for new applications to monitor and manage transmission risk. “We don’t really know where the technology is going to go, and what we might be able to do and understand,” she says. “A few years down the line, you might be able to take your smartphone out and cough into it” for a diagnosis.
Funding for the Virome of Manhattan project is provided by the Defense Advanced Research Projects Agency (DARPA) and the National Science Foundation. Additional funding was provided by a pilot grant from the National Institute of Environmental Health Sciences (NIEHS) Center for Environmental Health in Northern Manhattan.
