Category: Infectious Agents Surveillance Report (IASR)
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The Topic of This Month Vol.34 No.6 (No.400)

Legionellosis, January 2008-December 2012

(IASR 34: 155-157, June 2013)


Legionellosis is an infectious disease caused by Gram-negative bacteria belonging to the genus Legionella.  It is a respiratory tract infection and the bacteria multiply within alveolar macrophages.  There are two clinical types, severe form of pneumonia called Legionnaires’ disease and flu-like Pontiac fever.  As the symptoms of Legionella pneumonia are not unique, differentiation from other pneumonias by symptoms alone is difficult.  The first choices for chemotherapy are quinolones and macrolides.  Sudden worsening of the general condition may occur among patients, who were not treated with appropriate antibiotics.  Pontiac fever is a less severe form of infection and the symptom is like common cold.  Elderlies, newborns and immunocompromised persons constitute high-risk groups of legionellosis.

Legionella bacilli live within protozoa (amoeba) that inhabit water, moist soil, etc.  Optimum growth temperature is 36°C with permissive range of 20-45°C.

Incidence of legionellosis: Legionellosis is a category IV notifiable infectious disease in the National Epidemiological Surveillance of Infectious Diseases (NESID) under the first Diseases Control Law (  Physicians who have made diagnosis of legionellosis are obliged to notify all the cases.

From January 2008 to December 2012, 4,081 legionellosis patients (including 31 asymptomatic carriers) were reported (as of May 15, 2013) (Table 1).  The peak season of legionellosis was mostly July (Fig. 1).  More patients were reported from more populated prefectures as expected (  Number of patients per 100,000 was high in Toyama, Ishikawa, Okayama and Tottori Prefectures (Fig. 2).  The average patients’ age was 67.0 years, 65.7 years in males and 72.5 years in females.  While the patients’ ages were distributed widely from 0 year to 103 years, patients younger than 30 years were few (1.0%) (Fig. 3).  Males occupied 81% of the patients.  According to MMWR 60: 1083-1086, 2011, males were 64% of the patients in USA.  Occupations at high risk were reported to be mining and construction, manufacturing of metal materials, assembly and/or repair of transportation machines, and car driving, etc.  Symptoms are fever (92%), pneumonia (90%), cough (48%), dyspnea (44%), disturbance of consciousness (17%), diarrhea (9.8%), multiple organ failure (8.5%), and abdominal pain (2.5%) (percentage in parenthesis indicates percentage among the notified patients having the symptom indicated).  As for the location of infection, 3,962 cases (97%) were infected in Japan, 95 cases (2.3%) abroad and 24 cases (0.6%) unknown.

Methods of diagnosis: Of 4,081 cases, 3,928 (96%) were diagnosed by antigen detection in urine, 113 cases (2.8%) by bacterial culture, 69 (1.7%) by titration of serum antibody, 62 (1.5%) by PCR (including LAMP method), and 8 (0.2%) by the indirect fluorescent antibody method or by the enzyme-linked antibody method (Table 2 on p.157 of this issue).

While antigen detection in urine was used in a great majority, it can detect only Legionella pneumophila serogroup (SG) 1.  The LAMP assay that can detect a wide range of genus Legionella started to be covered by the medical insurance since October 2011.  In 2012, 5 cases were diagnosed by this method.

The number of deaths among the total cases was 134 (3.3%) for 2008-2012.  Among 4,023 patients having the record of the first medical consultation, there were 129 deaths.  It was noted that the longer was the delay from the first consultation to the definitive diagnosis, the higher was the fatality rate, i.e., 2.8% for 0-3 day delay, 4.2% for 4-6 day delay and 5.3% for ≥7 day delay.  Early diagnosis is important for saving lives of the patients.

Species of Legionella isolated by culture: In addition to the above 113 culture-positive cases, reported were additional 148 cases that included isolates provided to the Legionella Reference Center after the notification (see p. 161 of this issue).  Thus Legionella was isolated from total 261 cases.  Among them, there were 216 cases attributable to infection of L. pneumophila SG1.  Some such cases of infection with L. pneumophila SG1 were infected additionally with other Legionella species or serogroups, such as, L. feeleii (one case), L. rubrilucens (one case), L. pneumophila SG6 (two cases), and L. pneumophila SG6 and SG9 and untypable (one case).  There were 24 cases due to L. pneumophila other than L. pneumophila SG1; six cases each due to infection with SG2 and SG3, four cases due to infection with SG6, two cases each due to infection with SG5, SG10 and SG12, and one case each due to infection with SG9 and SG15.  Furthermore, there were one case of L. londiniensis, one case of L. longbeachae, and 19 cases of Legionella whose species were not identified. 

Outbreaks: Outbreaks that occurred in Japan during 2008-2012 involved 2 cases at a public bathing facility in Kobe City in January 2008 (IASR 29: 329-330, 2008); 2 cases at a welfare facility for the elderly in Okayama Prefecture in July 2008 (IASR 29: 330-331, 2008); 8 cases attributable to a bathing facility in a hotel in Gifu Prefecture in October 2009 (IASR 31: 207-209, 2010); 9 cases attributable to a bathing facility of a sports club in Yokohama City in September 2011; 3 cases attributable to a bathing facility in a hotel in Yamagata Prefecture in November 2012 (see p. 159 of this issue); and 9 cases attributable to a “one-day-trip hot spring” in Saitama Prefecture in November to December 2012 (see p. 157 of this issue).  There were 13 suspected clusters, each reporting 2-5 legionellosis patients that were found among those who used the same facilities or toured together.  In addition, after the tsunami associated with the Great East Japan Earthquake, legionellosis was reported among those who were rescued from drowning or engaged in debris processing (see p. 160 of this issue).

Control measures: Legionella infection occurs through inhalation of aerosols or dusts contaminated by Legionella.  The infection source includes spa pools, cooling towers, showers (IASR 31: 331-332, 2010 & 31: 332-333, 2010), hot water supply system, landscaping water, humidifiers (see p.169 of this issue), solar water-heaters (IASR 32: 113-115, 2011) and leaf molds (IASR 26: 221-222, 2005).  Biofilm growing on porous natural stones in a bath sometimes becomes a hotbed of Legionella (IASR 29: 193-194, 2008).

Principles of prevention of legionellosis include 1) prevention of microbial growth and biofilm formation, 2) removal of biofilm formed on equipments and facilities, 3) minimizing aerosol splash, and 4) minimizing of bacterial contamination from external sources.  For this, following measures should be taken.  Firstly, water should be disinfected (see p.168 of this issue), which should be checked by culture of microbes or by rapid tests (see p.165 of this issue).  The current hygienic standard of bath water that may pose risk of aerosol inhalation is Legionella counts less than 10 cfu per 100 ml (below the detection limit).  Secondly, the wall of bath rooms and inner surface of water tanks should be cleaned.  Removal of the biofilm can be checked by measuring adenosine-tri-phosphate (ATP) (see p.167 of this issue).  Thirdly, equipments and facilities should be designed so as not to splash aerosols.  Fourthly, those who clean the wall of bathrooms or hand leaf molds should wear a dust mask.

Hygienic control for prevention of legionellosis should follow guidelines, such as Legionella Control Measures (Ministry of Health, Labour and Welfare: MHLW), Building Hygiene (MHLW), Guidelines for prevention of legionellosis (3rd Ed., Building Management Education Center), Introduction to hygienic maintenance of storage-type hot-water supply equipment (1st Ed., Japan Water Facilities Environmental Hygiene Association).

For prevention of legionellosis, infection sources should be identified by analyzing the data obtained from the pulsed-field gel electrophoresis and sequence-based typing using Legionella obtained from both patients and environment (see p.161 of this issue).  With such information, disinfection and/or removal of Legionella can be effectively onducted.


The statistics in this report are based on 1) the data concerning patients and laboratory findings obtained by the National Epidemiological Surveillance of Infectious Diseases undertaken in compliance with the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections, and 2) other data covering various aspects of infectious diseases.  The prefectural and municipal health centers and public health institutes (PHIs), the Department of Food Safety, the Ministry of Health, Labour and Welfare, and quarantine stations, have provided the above data.


Copyright 1998 National Institute of Infectious Diseases, Japan