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Legionnaires’ disease organism sources largely unknown
Despite surveillance programs, research suggests the source of organisms in the majority of Legionnaires’ disease cases remains unknown, according to a study published in Emerging Infectious Diseases.
“After a large outbreak of [Legionnaires’ disease (LD)] at a flower show in Bovenkarspel, the Netherlands, in 1999, prevention and control of Legionella spp. infections became a national concern in the Netherlands,” Jeroen W. Den Boer, MD, public health physician and epidemiologist, Regional Public Health Laboratory Kennemerland, Haarlem, the Netherlands, and colleagues wrote. “In 2002, a National Legionella Outbreak Detection Program (NLODP) was implemented on the basis of a report that LD outbreaks are often preceded and followed by small clusters of solitary cases.
“For evaluation of transmission pathways, infection sources are sampled, and genotypes of Legionella strains found in these samples are compared with those of clinical isolate(s) from the patient(s) associated with that source.”
The researchers studied 1,991 patients who contracted Legionnaires’ disease domestically and were reported to the NLODP from 2002 to 2012. They conducted 1,484 investigations to find the source of the Legionella organisms, with 24.7% of these potential sources testing positive for Legionella spp. Only 41 patients were matched by genotype to a Legionella strain found at a source location, the researchers wrote.
Based on a questionnaire provided by public health physicians and nurses to patients and their families, more than half of source investigations (n = 762) were conducted at residences, though only 20.3% of these investigations yielded positive tests for Legionella spp., according to Den Boer and colleagues. Other source types tested positive for Legionella spp. a greater percentage of the time, but were tested less frequently. They included wellness centers (27 of 37 positive source samples), hospital/health care settings (46 of 90), cooling towers (19 of 43), hotels (8 of 20), sports facilities (10 of 29) and swimming pools (13 of 40).
The researchers said they identified 105 clusters related to 266 patients, with the most common clusters found in garden centers (n = 27), hospital/health care settings (n = 17), residences (n = 10) and wellness centers (n = 9).
Garden centers were among the most frequently reported potential sources of LD infection and were associated with 25.7% of identified clusters, the researchers wrote. They said this indicated that patients with LD frequently visited these centers during the 2- to 14-day period before symptom onset.
“However, only eight out of 86 investigated garden centers were found positive for Legionella spp. during source investigations,” Den Boer and colleagues wrote. “Several studies have shown the presence of Legionella spp. in potting soil samples.
“These findings suggest that potting soil samples from garden centers identified as potential sources of infection for patients with LD should be examined closely. Also, a need exists for further investment in improving laboratory techniques for detection of Legionella spp. in clinical samples with a high background of microbial flora such as soil.” – by David Jwanier
Disclosure: Infectious Disease News was unable to confirm disclosures at the time of publication.