Large community-acquired Legionnaires’ disease outbreak caused by Legionella pneumophila serogroup 1, Italy, July to August 2018

Abstract

In July 2018, a large outbreak of Legionnaires’ disease (LD) caused by Legionella pneumophila serogroup 1 (Lp1) occurred in Bresso, Italy. Fifty-two cases were diagnosed, including five deaths. We performed an epidemiological investigation and prepared a map of the places cases visited during the incubation period. All sites identified as potential sources were investigated and sampled. Association between heavy rainfall and LD cases was evaluated in a case-crossover study. We also performed a case–control study and an aerosol dispersion investigation model. Lp1 was isolated from 22 of 598 analysed water samples; four clinical isolates were typed using monoclonal antibodies and sequence-based typing. Four Lp1 human strains were ST23, of which two were Philadelphia and two were France-Allentown subgroup. Lp1 ST23 France-Allentown was isolated only from a public fountain. In the case-crossover study, extreme precipitation 5–6 days before symptom onset was associated with increased LD risk. The aerosol dispersion model showed that the fountain matched the case distribution best. The case–control study demonstrated a significant eightfold increase in risk for cases residing near the public fountain. The three studies and the matching of clinical and environmental Lp1 strains identified the fountain as the source responsible for the epidemic.

A community-acquired Legionnaires’ disease outbreak caused by Legionella pneumophila serogroup 2: an uncommon event, Italy, August to October 2018

“…Heavy thunderstorms occurred in the days immediately before the occurrence of the first cases, creating conditions which could have been favourable to the production and spread of infectious aerosols. Similar conditions were observed in an Lp outbreak that occurred in the same year between July and August in Lombardy region in the metropolitan area of Milan [34]. Although the area where the cases occurred has many industrial plants equipped with cooling systems, Lp2 ST1455 colonies were not detected in any of the sampled cooling towers.…”

“…Cases and incidence rate of Legionnaires' disease cases per million inhabitants, Brescia province,Italy, 2015Italy, -2018 …”

Performance of Legiolert Test vs. ISO 11731 to Confirm Legionella pneumophila Contamination in Potable Water Samples

“…In Italy in 2018, the incidence of Legionnaires' disease was 4.9 cases per million inhabitants, 2964 notified cases [11], and in the European network for Legionnaires' disease surveillance, Italy ranked first in terms of the number of reported cases [12]. In addition, in 2018 two important outbreaks occurred in Italy that required increased environmental monitoring ( [13]; data unpublished).…”

Effects of climate changes and road exposure on the rapidly rising legionellosis incidence rates in the United States

“…While precipitation promotes road exposure mainly in sporadic cases that account for 95% of all legionellosis cases in the US in recent decade [Han XY, unpublished, 2021], it may also aid outbreaks in certain settings. For example, in a recent outbreak investigation, heavy rainfalls were noted to precede a fountain-related community outbreak by 1 to 2 weeks to suggest a promotive role [45]. Presumably, in the context of this discussion, the rainfalls could have attenuated sunlight, produced more aerosols, and/or raised atmospheric humidity to aid the survival of aerosols and bacteria for more exposure.…”