WHO reports Legionellosis outbreak in Argentina

As of 3 September 2022, a cluster of 11 cases of severe pneumonia, including four deaths, have been reported in San Miguel de Tucumán city, Tucuman Province,

Argentina. Legionella spp. was isolated in the samples from four cases. Legionellosis is a pneumonia-like illness that varies in severity from mild febrile illness to a serious and sometimes fatal form of pneumonia. Cases were initially reported as being pneumonia of unknown cause. Legionella bacteria was identified as the causative organism on 3 September.

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

Outbreak overview

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

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

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

As of 3 September 2022, 11 cases have been identified, four of whom have died (three health workers). Eight of the 11 reported cases are health workers of the same health facility. The median age of the cases is 45 years; seven are male. Ten cases had underlying conditions and/or risk factors for severe disease, including the four reported deaths. Four cases are still hospitalized as of 3 September. Contacts of the cases are under follow-up and, to date, none have developed symptoms.

Laboratory results

Blood, respiratory and tissues samples were obtained from the 11 cases. Preliminary tests conducted at the local Public Health Laboratory were negative for respiratory viruses, and other viral, bacterial, and fungal agents. On 31 August, samples from the initial 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 per its acronym in Spanish) - for additional testing 4 . As of 3 September 2022, negative results have been obtained for COVID-19 (RT-PCR), Influenza, detection of antibodies for Coxiella, urinary antigen for Legionella spp., panel of 12 respiratory viruses, hantavirus (Elisa IgM), histoplasma (RT-PCR), Yersinia pestis (PCR) and micro agglutination for leptospirosis.

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

Epidemiology of Legionellosis

Legionellosis is a generic term describing the pneumonic and non-pneumonic forms of infection with the Legionella species of bacteria. Legionellosis varies 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 recorded in some outbreaks). It is an important cause of community- and hospital-acquired pneumonia; and although uncommon, Legionnaires may cause outbreaks of public health significance. Initially, symptoms are fever, mild cough, loss of appetite, headache, malaise and lethargy, with some patients also experiencing muscle pain, diarrhoea and confusion. The severity of Legionnaires’ disease ranges from a mild cough to rapidly fatal pneumonia. Untreated Legionnaires’ disease usually worsens during the first week.

Mortality from Legionnaires’ disease depends on the severity of the disease, the use of antibiotic treatment, the setting where Legionella was acquired, and whether the patient has underlying conditions, including immunosuppression. The death rate may be as high as 40–80% in untreated immunosuppressed patients and can be reduced to 5–30% through appropriate case management, depending on the severity of the clinical signs and symptoms. Overall, the death rate is usually between 5–10%.

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