Most H1N1 Cases Go Unreported

The reported number of confirmed H1N1 “swine flu” cases nationwide is likely a considerable underestimation of the total sum of actual illnesses, according to a recent study conducted by researchers at the Center for Disease Control and Prevention and Harvard School of Public Health.

The study, published in the CDC journal “Emerging Infectious Diseases,” estimated that the total number of swine flu cases in the United States between April and July 2009 ran up to 140 times higher than the number of cases confirmed by laboratory tests.

Researchers on the study concluded that the actual number of cases hovered anywhere from 1.8 million to 5.7 million cases: far more than the 43,677 lab-confirmed cases that were identified nationwide through July, according to the paper. “Not every case, by a long shot, got reported...Once the number of cases grew, issues of capacity made testing and reporting even more significant,” wrote Marc Lipsitch, professor of epidemiology at the Harvard School of Public Health and a co-author of the study, in an e-mail.

“There are limited resources for testing and exponentially growing numbers of people to be tested,” Lipsitch wrote.

Though it is difficult to find accurate epidemiological numbers, more exact estimation will help to inform vaccine and treatment recommendation to improve predictions of future spread, Lipsitch wrote. The CDC reported on October 23 that the fast-moving “swine flu” pandemic had spread to 177 countries worldwide and that flu activity remains widespread in 46 U.S. states. The latest weekly report from the World Health Organization only accounts for 440,000 laboratory confirmed cases of pandemic H1N1 influenza through the end of October throughout the globe, admitting that the case count is likely to be significantly lower than the actual number of cases as “many countries have stopped counting individual cases.”


According to David S. Rosenthal ’59, director of Harvard University Health Services, UHS has seen between 40 and 60 cases a week of influenza-like illness.

Explaining possible reasons why swine flu cases could go unnoticed, Rosenthal said that many people are asymptomatic or may suffer less severe symptoms after gaining a level of passive immunity from being exposed to the disease in roommates or colleagues.

“The good news is that so far, [swine flu] is no worse than the seasonal flu... the population of undergraduates, students seem to be managing well.” Robert J. Blendon, professor of Health Policy and Political Analysis at the Harvard School of Public Health defended the importance of studying unreported flu cases in an interview this week, saying that they could be important in raising public awareness.

“These debates about how many cases there are, are very important...a very widespread disease will prompt people to take many precautions,” he said. “If they are less worried, they will take fewer precautionary steps that they might not have done.”l