Nursing home outbreak of influenza A (H3N2): evaluation of vaccine efficacy and influenza case definitions.

OBJECTIVES

Describe an outbreak of influenza A (H3N2); provide an analysis of vaccine efficacy; measure the sensitivity, specificity, and positive predictive value of 3 clinical case definitions of influenza.

SETTING

A nursing home in Washington County, Maryland. The outbreak involved 52 residents (attack rate = 47.7%) and at least 10 of 140 employees (minimum attack rate = 7.1%).

RESULTS

Twenty-five residents exhibited a 4-fold or greater increase in titer to influenza A/Sichuan/2/87. Vaccine efficacy was measured at -7.1%, suggesting that the influenza vaccine in 1988/1989 did not offer optimal protection against influenza A infection for the institutionalized elderly.

CONCLUSIONS

The outbreak was a clear indicator of the need for rapid diagnosis. With the use of rapid diagnostic tests, influenza A could have been detected in time to use amantadine.