Community outbreak of legionellosis and an environmental investigation into a community water system

Abstract

During two legionellosis outbreak investigations, one at a geriatric centre and the other in high-rise housing for seniors, it was observed that additional cases of legionellosis occurred in nearby smaller residential settings. This apparent geographical cluster of legionellosis occurred in the same general area of a community water storage tank. No potential airborne sources in or near the area could be identified, but a community water system storage tank that was centrally located among case residences spurred an investigation of water-quality factors in the identified investigation area. Conditions conducive for Legionella growth, particularly low chlorine residuals, were found. The rate of legionellosis among residents aged ⩾50 years in the investigation areas (61·0 and 64·1/100 000) was eight times higher than in the rest of the service area (9·0/100 000) and almost 20 times higher than the statewide annual average incidence rate (3·2/100 000). A water mains flushing programme in the area was launched by the water utility, and water samples taken before and during flushing found L. pneumophila.

Occurrence of culturableLegionella pneumophilain drinking water distribution systems

“…Diverse Legionella spp., including L. pneumophila , L. pneumophila sg1, and L. anisa , were identified. At least one outbreak has been associated with a community water system storage tank that had low (<0.2 mg/L) free chlorine residuals (Cohn et al, ). Additional monitoring of drinking water storage tanks and reservoirs may be warranted.…”

“…Although outbreaks typically occur in building water systems and cooling towers, potable water utilities typically do not monitor for this important pathogen. One outbreak, however, was associated with a community water system storage tank that had a low (<0.2 mg/L) free chlorine residual (Cohn et al, ).…”

The sporadic nature of Legionella pneumophila, Legionella pneumophila Sg1 and Mycobacterium avium occurrence within residences and office buildings across 36 states in the United States

“…Sporadic detections pose a monitoring challenge in assessing the relationship between occurrence and illness. The Cohn et al (2015) publication on community legionellosis outbreaks in New Jersey illustrates a situation where the sporadic community-acquired legionellosis cases exceeded the case rate of two outbreak episodes in a single geographical area over a 5year period. During one of the outbreak investigations, no Legionella sp.…”

Rolling epidemic of Legionnaires’ disease outbreaks in small geographic areas

“…In the US, there have recently been two examples of neighbourhood-scale or city-scale outbreaks, which were linked directly to the potable water distribution system. In New Jersey, the drinking water was investigated because there were no cooling towers in the area that could explain the outbreak 52 . The second example is Flint Michigan, where corrosion in the distribution system led to city-wide proliferation of Legionella , particularly at the ends of the main water pipes where concentrations of disinfectant had progressively decreased before entering plumbing in homes 53 .…”