Article Abstract

A combined outbreak of Legionnaires’ disease and Pontiac fever related to an ultrasonic humidifier contaminated with Legionella pneumophila serogroup 1, Nanjing City, China, 2012

Authors: Lian Zhou, Liangliang Cui, Lilin Xiong, Xuefei Du, Yong Yu, Xiaojing Sheng, Xiaodong Chen


Background: On June 14, 2012, more than ten female workers from factory L were reported for illness with fever, chest tightness, myalgia, and non-productive cough within 1 day in Nanjing City, China. To verify and control the outbreak, we conducted this epidemiological investigation.
Methods: A face to face interview was used for the case finding and information collecting, and conducted to the total of 45 staffs by a structured questionnaire. Urine samples from all cases were collected and tested for Legionella pneumophila serogroup 1 (LP1) antigen, and five sera samples were tested for Legionella antigen and Legionella antibody. Two cooling water samples from cabinet air conditioner and three from the humidifier were collected to test Legionella bacteria. The attack rate (AR) was calculated for overall and for different production lines, individually.
Results: A total of 15 cases, 9 suspected cases and 6 confirmed cases, 8 Legionnaires’ disease (LD) cases and 7 Pontiac fever (PF) cases, 5 inpatients and 10 outpatients, with an overall AR of 75% (15/20, one worker was for personal leave) were identified for illness onset on June 13, 2012. Six of 15 cases urine samples were tested positive for LP1; 1 of 5 inpatients was positive for Legionella antibody and another for antigen positive. Legionella bacteria was isolated from one water sample from the humidifier and confirmed as LP1.
Conclusions: A combined outbreak of LD and PF caused by a contaminated humidifier was demonstrated and it was the first report and in China.