As of September 3, 2022, a cluster of 11 cases of severe pneumonia, including four deaths, have been reported in the city of San Miguel de Tucumán, Tucuman Province, Argentina. Legionella spp. was isolated in the samples from four cases. Legionellosis is a pneumonia-like illness that varies in severity from a mild febrile illness to a severe and sometimes fatal form of pneumonia. The cases were initially reported as pneumonia of unknown cause. The bacterium Legionella was identified as the causative organism on September 3. All cases presenting with bilateral pneumonia, fever, myalgia, abdominal pain and dyspnoea between 18 and 25 August 2022 and epidemiologically linked to one health unit. Of the 11 cases, eight are health workers at the facility. three are patients of the health institution. 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. Epidemic overview On 29 August 2022, WHO was informed by the Ministry of Health of Argentina of a report by the Ministry of Public Health of the Province of Tucuman, of a cluster of six cases of bilateral pneumonia without an etiological cause identified in the city of San Miguel de Tucumán, Tucuman Province, Argentina 1 .All six cases were linked to a private health facility in the city of San Miguel de Tucumán, with onset of symptoms between August 18 and 22, 2022. The six cases included five health workers and one patient admitted to the clinic for an unrelated condition and then in the intensive care unit after the onset of 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 health care workers from the same private health facility, aged 30 to 44 – with similar signs and symptoms to the original six cases identified 2. The onset of 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 picture to the previous cases 3. As of September 3, 2022, 11 cases have been identified, four of whom have died (three healthcare workers). Eight of the 11 reported cases are health workers from the same health facility. The median age of 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 are still hospitalized as of September 3. The contacts of the cases are being monitored and, to date, none have developed symptoms. Laboratory results Blood, respiratory and tissue samples were obtained from the 11 cases. Preliminary tests done at the local Public Health Laboratory were negative for respiratory viruses and other viral, bacterial and fungal agents. On August 31, samples from the original 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 additional tests 4 . As of September 3, 2022, negative results have been obtained for COVID-19 (RT-PCR), influenza, antibody detection for Coxiella, urinary antigen for Legionella spp., panel of 12 respiratory viruses, handavirus (Elisa IgM), histoplasmosis ( RT-PCR ), Yersinia pestis (PCR) and microarray for leptospirosis. Further analyzes of two bronchoalveolar lavage samples by highly sensitive total DNA sequencing (metagenomics) found counts 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 analyzed by metagenomic sequencing and analyzed by four different bioinformatic methods, they produced results consistent with Legionella pneumophila. Confirmation of these results is expected upon completion of sequencing procedures. This laboratory result supports evidence consistent with Legionnaires’ disease. Blood culture and seroconversion tests are still being performed to complete the diagnosis of Legionella infection.
Epidemiology of Legionellosis Legionellosis is a general term that describes the pulmonary and non-pulmonary forms of infection by the Legionella species of bacteria. The severity of legionellosis varies from mild to severe 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 a major cause of community-acquired and hospital-acquired pneumonia. and although uncommon, Legionnaires’ may cause outbreaks of public health importance. Initially, symptoms are fever, mild cough, loss of appetite, headache, malaise, and lethargy, while some patients also experience 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 during the first week. Mortality from Legionnaires’ disease depends on the severity of the disease, the use of antibiotic therapy, the environment where the Legionella was acquired, and whether the patient has underlying conditions, including immunosuppression. The case fatality rate can 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 clinical signs and symptoms. Overall, the mortality rate is usually between 5-10%. In response to the detection of the bilateral pneumonia cluster, health authorities in the province of Tucuman coordinated cluster investigation activities, including case surveillance, tracing the source(s) of infection, active case finding to identify additional cases, and contact tracing. Preliminary investigations indicated that no secondary cases were identified. Like Legionella spp. has been identified as the cause of this outbreak, the following public health measures were implemented:

Risk assessment and suspension of health care activities in health facilities. Enhanced surveillance including active and passive incident detection. Biological and environmental sampling and laboratory testing, including bacterial isolation and metagenomics. Case isolation and clinical patient care. Contact identification, support and tracking. Hazard 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 is providing technical support for the outbreak investigation, including advice on sampling, environmental assessment, clinical management, and infection control and prevention (IPC) measures.