Green onions that were apparently contaminated before arrival at the restaurant caused this unusually large foodborne outbreak of hepatitis A. The inclusion of contaminated green onions in large batches that were served to all customers contributed to the size of the outbreak.

Ongoing viral strain surveillance facilitated the rapid implementation of control measures. Incorporation of molecular epidemiologic methods into routine hepatitis A surveillance would improve the detection of hepatitis A outbreaks and increase our understanding of hepatitis A epidemiology in the United States.

No abstract

In July 1995 we investigated a pneumonia outbreak in a Pennsylvania town. We conducted epidemiological and molecular microbiological studies to determine the outbreak source and interrupt transmission of disease. Legionnaires' disease (LD) was quickly identified by urine antigen testing, and a newly developed immunohistochemical stain confirmed nosocomial transmission to a hospital inpatient. LD was confirmed in 22 patients. Case-patients were more likely than controls to have been within 1,000 feet of the hospital (matched odds ratio, 21.0; 95% confidence interval, 2.9-368) during the 2 weeks prior to illness. Legionella pneumophila serogroup 1 (Lp-1) was isolated from hospital cooling towers (CTs) and rooftop air samples but not from hospital potable water or community CTs. Hospital CT and air Lp-1 isolates matched all five patient isolates by monoclonal antibody, arbitrarily primed polymerase chain reaction, and pulsed-field gel electrophoresis subtyping. Strategies to prevent LD must include minimizing transmission from CTs.