Legionellosis – Argentina

An explosion at a glance

As of September 3, 2022, a cluster of 11 cases of severe pneumonia, including four deaths, were reported in the city of San Miguel de Tucuman, Tucuman Province, Argentina. Legionella spp. was isolated in the samples from four cases. Legionellosis is a pneumonia-like illness that ranges in severity from a mild febrile illness to a serious and sometimes fatal form of pneumonia. Initially, cases of pneumonia of unknown cause were reported. The Legionella bacterium was identified as the causative agent on September 3.

All cases presented with bilateral pneumonia, fever, myalgia, abdominal pain, and dyspnea between August 18 and 25, 2022, and were epidemiologically linked to a single health facility. Of the 11 cases, eight were healthcare workers at the facility; three are patients of the health facility. Three of the four deaths were among healthcare workers.

Health authorities are coordinating cluster investigation activities, active case finding to identify additional cases, contact tracing, and public health activities to limit further spread.

Overview of the epidemic

On 29 August 2022, WHO was notified by the Ministry of Health of Argentina of a report from the Ministry of Public Health of the Province of Tucuman on a cluster of six cases of bilateral pneumonia without an etiological cause identified in the city of San Miguel de Tucuman, Tucuman Province, Argentina 1 .All six cases were linked to a single private health facility in the city of San Miguel de Tucuman, with symptoms appearing between August 18 and 22, 2022. The six cases involved five health workers and one patient who was admitted to the clinic for an unrelated condition and then in the intensive care unit after developing pneumonia. In addition to bilateral pneumonia, all cases presented with fever, myalgia, abdominal pain, and dyspnea.

On September 1, three additional cases were identified through active case finding – all healthcare workers from the same private healthcare facility, aged 30 to 44 years – with similar signs and symptoms as the first six identified cases 2. The onset of symptoms for these cases was between August 20 and 25, 2022.

Between 2 and 3 September, two additional cases were identified, an 81-year-old man and a 64-year-old man, both with comorbidities, who were hospitalized and presented with a similar clinical presentation to the previous 3 cases.

As of September 3, 2022, 11 cases have been identified, four of whom have died (three healthcare workers). Eight of the 11 registered cases are of health workers from the same medical facility. The average age of the cases is 45 years; seven are men. Ten cases had underlying conditions and/or risk factors for severe disease, including the four reported deaths. Four cases were still hospitalized as of September 3. The contacts of the sick are being followed up and to date there are no symptoms.

Laboratory results

Blood, breath and tissue samples were taken from 11 cases. Preliminary tests performed at the local public health laboratory were negative for respiratory viruses and other viral, bacterial, and fungal agents. On August 31, samples from the first six cases were sent to the National Reference Laboratory – the Administration of National Laboratories and Health Institutes (Administración Nacional de Laboratorios e Institutos de Salud – ANLIS according to its acronym in Spanish) – for further investigation 4 . As of September 3, 2022, negative results were obtained for COVID-19 (RT-PCR), influenza, detection of Coxiella antibodies, urine antigen for Legionella spp., panel of 12 respiratory viruses, hantavirus (Elisa IgM), histoplasma ( RT-PCR), Yersinia pestis (PCR) and micro agglutination for leptospirosis.

Further analyzes of two bronchoalveolar lavage samples by highly sensitive total DNA sequencing (metagenomics) found readings consistent with Legionella spp. On September 3, 2022, ANLIS reported that 16S ribosomal gene amplification products for Legionella spp. of the two bronchoalveolar lavage samples sequenced by metagenomics and analyzed by four different bioinformatics methods yielded results consistent with Legionella pneumophila. Confirmation of these results is expected after completion of the sequencing processes. This laboratory result supports evidence consistent with Legionnaires’ disease. Blood culture and seroconversion tests continue to be performed to complete the diagnosis of Legionella infection.

Epidemiology of legionellosis

Legionellosis is a general term describing pneumonic and non-pneumonic forms of infection with Legionella bacteria. Legionellosis ranges in severity from mild to serious and can sometimes be fatal.

Legionnaires’ disease, the pneumonic form, has an incubation period of 2 to 10 days (but up to 16 days have been reported in some outbreaks). It is an important cause of community-acquired and hospital-acquired pneumonia; and although uncommon, Legionnaires’ disease can cause outbreaks of public health concern. Initially, symptoms include fever, mild cough, loss of appetite, headache, malaise, and lethargy, with some patients also experiencing muscle pain, diarrhea, and confusion. The severity of Legionnaires’ disease ranges from a mild cough to rapidly fatal pneumonia. Untreated Legionnaires’ disease usually gets worse in the first week.

Mortality from Legionnaires’ disease depends on the severity of the disease, the use of antibiotic treatment, the environment in which Legionella is acquired, and whether the patient has underlying diseases, including immunosuppression. Mortality can reach 40–80% in untreated immunosuppressed patients and can be reduced to 5–30% by appropriate case management, depending on the severity of clinical signs and symptoms. Overall, the mortality rate is usually between 5-10%.

In response to the discovery of a cluster of bilateral pneumonia, health authorities in the province of Tucuman coordinated cluster investigation activities, including case tracking, tracing the source(s) of infection, active case finding to identify additional cases, and contact tracing. Preliminary investigations indicate that no secondary cases have been identified.

Since Legionella spp. has been identified as the etiology of this outbreak, the following public health measures have been implemented:

• Risk assessment and suspension of health activity in the health facility.
• Enhanced surveillance, including active and passive case detection.
• Biological and environmental sampling and laboratory testing, including bacterial isolation and metagenomics.
• Isolation of cases and clinical care of patients.
• Contact identification, support and monitoring.
• Risk Communication

With the support of national health authorities, environmental samples are collected to determine the source of contamination and to urgently implement prevention and control measures. Health authorities also implement internal and external communication strategies for health professionals and the community.

The Pan American Health Organization (PAHO)/WHO provided technical support for outbreak investigation, including advice on sampling, environmental assessment, clinical management, and infection control and prevention (IPC) measures.