Probable Person-to-Person Transmission of Legionnaires’ Disease

Abstract

To the Editor: Legionnaires' disease is an often severe form of pneumonia that is typically acquired by susceptible persons (e.g., elderly persons and smokers) through inhalation of aerosols that contain legionella species. 1-4 A cluster of cases of this disease occurred in Vila Franca de Xira, Portugal, in 2014. 5 One of the first cases of disease in this cluster occurred in a 48-year-old man (Patient 1), a smoker, who had been employed since October 6, 2014, as a maintenance worker at an industrial cooling tower complex in Vila Franca de Xira that was subsequently found to be contaminated with Legionella pneumophila. 5 He returned to the home that he shared with is mother in Porto (approximately 300 km from Vila Franca de Xira) on October 11 and again on the evening of October 19 (Fig. 1). His symptoms began on October 14, and on October 19, he had severe respiratory symptoms, including an intense cough. During that night, his mother (Patient 2) took care of him until he was admitted to the hospital (Centro Hospitalar do Porto) approximately 8 hours later. On October 22, he was transferred to another hospital to receive extracorporeal membrane oxygenation. On October 27, Patient 2, who was a previously healthy 74-year-old woman, began to report fever, cough, and loss of appetite. She was admitted to the same hospital on November 3 with septic shock due to pneumonia, and she died on December 1. Patient 1 died on January 7, 2015. Urine specimens obtained from both patients showed positive results on testing for legionella

Multiple major disease-associated clones ofLegionella pneumophilahave emerged recently and independently

“…L. pneumophila has been isolated from human feces (Rowbotham 1998) and is regularly isolated from the sputa of Legionnaires' disease patients, suggesting that human infection may not actually be a dead end. Further support for this has also come from a recently reported case of probable person-to-person transmission of Legionnaires' disease (Correia et al 2016). Scenarios involving human-to-human transmission and/or human-to-environment transmission could simultaneously explain why these specific strains have emerged recently, spread widely, and are primarily associated with human infection.…”

“…It is thought that the conservation of signaling pathways and cellular functions from protozoa to higher eukaryotes allows Legionella to also infect human alveolar macrophages. However, although humans have traditionally been considered a dead-end host for Legionella, one probable case of person-to-person transmission has recently been reported (Correia et al 2016).…”

Vital Signs: Deficiencies in Environmental Control Identified in Outbreaks of Legionnaires’ Disease — North America, 2000–2014

“…Transmission from these water systems to humans requires aerosol generation, as can occur from showerheads, cooling towers, hot tubs, and decorative fountains (7). Only one case of possible person-to-person transmission has been reported (8). Legionnaires' disease is typically diagnosed by a Legionella urinary antigen test or culture of lower respiratory secretions using selective media; epidemiologic links to environmental sources can be confirmed when isolates from clinical and environmental specimens match by molecular typing (9).…”

Type II Secretion Is Necessary for Optimal Association of the Legionella-Containing Vacuole with Macrophage Rab1B but Enhances Intracellular Replication Mainly by Rab1B-Independent Mechanisms

“…Human infection occurs mainly by the inhalation of contaminated water droplets originating from a wide range of aerosolgenerating devices (12,13). Yet the first case of person-to-person spread was reported in 2016 (14). In the lungs, L. pneumophila invades and grows in the resident macrophage population and ultimately triggers severe inflammation (3).…”