Shigella sonnei waterborne transmission in a state park--New Jersey 2012

Background: On June 24, 2012 an emergency department physician called the New Jersey Department of Health (NJDOH) to report two unrelated families being evaluated for diarrheal illnesses. These patients tested positive for Shigella sonnei and reported swimming in the same lake at a NJ state park. NJDOH investigated to identify additional cases and to determine possible infection sources. Methods: We reviewed reported gastrointestinal illnesses to identify additional associated cases. We defined (1) confirmed cases as gastrointestinal illnesses with positive cultures for S. sonnei and lake exposure, (2) probable cases as gastrointestinal illnesses and lake exposure, and (3) secondary cases as gastrointestinal illnesses epidemiologically linked to a confirmed case. Cases were interviewed with a developed targeted questionnaire. The lake's facilities- a concession stand, septic system, potable water system, and swimming area- were inspected. Results/Conclusions: We identified 12 confirmed, 13 probable and 3 secondary cases. For confirmed cases, illness onset dates range from June 21-24 and lake exposure from June 20-22. Investigation findings ruled out septic system breaches, failure of potable water system and contamination of concession food items. Findings suggested that Shigella bacteria were most likely introduced into the lake by a fecal contamination from visitors. Due to warm weather and staff shortage, a high volume of visitors were confined to a small area of the lake and likely facilitated disease transmission which was interrupted by the lake's weather-related closure on June 21. This outbreak underscores the importance of recognizing recreational waterborne illnesses and promoting appropriate measures to limit and prevent such illnesses.