Study supports value of social restrictions during influenza pandemics

Aug 8 2007

Although physicians have imposed quarantine orders since at least 1374, when the Port of Venice officially isolated foreigners and shippers for 40 days to keep out infectious scourges, there has been no definitive evidence that public health measures like quarantining the sick and isolating people after exposure to ill people would save lives during an influenza pandemic.

Until now.

In a study published in the Aug. 8 Journal of the American Medical Association, a team of University of Michigan medical historians and epidemiologists from the federal Centers for Disease Control and Prevention say that social restrictions allowed 43 U.S. cities to save thousands of lives during the Spanish influenza pandemic of 1918-1919.

Although these urban communities had neither effective vaccines nor antiviral medicines, they were able to organize and execute a suite of classic public health measures , called non-pharmaceutical interventions or NPIs , before the pandemic gained full force.

The new study finds that cities whose NPIs were sustained and layered with multiple tactics had the best outcomes. In addition to quarantine and isolation, the NPIs examined in this study were school closures and cancellation of public gatherings.

"Public health is everyone's responsibility. In a world faced by the threat of newly emerging and re-emerging infectious diseases, it is critical to determine if costly and potentially socially harsh NPI measures can save lives and reduce the numbers of those infected," says lead author Howard Markel, M.D., Ph.D., the George E. Wantz Distinguished Professor of the History of Medicine, professor of pediatrics and communicable diseases, and director of the U-M Center for the History of Medicine. "Now we know the answer is yes."

Markel adds that in today's world, implementing these measures in a layered, sustained fashion would also provide a cushion of time for the development and distribution of effective vaccines and antivirals, while reducing the crush on essential infrastructure.

"By better understanding what worked in the past, we can better prepare for the future," says senior author Martin Cetron, M.D., director of the CDC's Division of Global Migration and Quarantine. "Communities that were most successful during the 1918 pandemic quickly enacted a variety of measures. Those planning for the next pandemic need to carefully consider how to best use these strategies to protect people and decrease the potential impact of the next pandemic in their communities."

The 43 cities in the study were scattered from coast to coast and represented a combined population of approximately 23 million. In an exhaustive review of 1,144 primary and secondary sources that included U.S. census data, municipal records, newspapers and handbills covering a 24-week period , Sept. 8, 1918 through Feb. 22, 1919 , the researchers identified which NPIs were used in each city and when officials turned them on and off.

Using both actual death rates from pneumonia and influenza, and baseline rates for what would have been normal without a pandemic, the researchers found there were 115,340 excess pneumonia and influenza deaths attributable to the pandemic in these cities during the period studied. In comparing the death rates to when NPIs were turned on and off, they found that NPIs did mitigate the death rate, with a statistically significant association between increased duration of NPIs and reduced mortality.

Further, they discovered that city-to-city variation in mortality was associated with the timing, duration and combination of NPIs. St. Louis, Missouri, for example, closed schools and cancelled public gatherings relatively early in the pandemic and sustained these measures for about 10 weeks. The analysis shows that St. Louis had one of the largest drops in mortality while the NPIs were in force.

As a whole, the study's findings contrast markedly with the conventional wisdom that the Spanish Flu ravaged the United States and elsewhere, with little that could be done to stop its deadly toll.

Markel predicts that NPI measures will be socially painful in the next pandemic, but that the public's acceptance of NPIs is essential.