Deconstructing the CDC’s ‘Snapshot’ Estimates

Ryan McNeill | Reuters | September 7, 2016

THE SOURCE: The Centers for Disease Control and Prevention, with headquarters in Atlanta, Georgia, released estimates of deaths from drug-resistant infections that Reuters found could be off by more than 30 percent. REUTERS/Tami Chappell

In 2013, the U.S. Centers for Disease Control and Prevention released estimates of how many people in the country die every year from antibiotic resistant infections: 23,000. The agency estimates that an additional 15,000 die annually from Clostridium difficile, an infection linked to long-term antibiotic use. The estimates, the agency said at the time, provided the “first snapshot of the burden and threats posed by antibiotic-resistant germs having the most impact on human health.”

Since then, the estimates have been cited by untold numbers of media outlets and scholarly reports. A Google search for the estimates can yield nearly 100,000 hits. Reuters took a close look at how the agency arrived at its numbers and made a surprising discovery: They are based on so little hard data that they could be off by more than 30 percent – more than 10,000 people – in either direction.

The statistical uncertainty is a byproduct of the nation’s lack of a unified surveillance system. No one at the state or federal level knows how many people are dying from drug-resistant infections. Absent hard numbers, the agency turned to studies that rely on statistical sampling, whereby a subset of the population is studied and the results are extrapolated to cover the entire country. Statistical sampling is common. Precision depends on the size of the sample. The larger the sample, the greater the precision....