Impact of Legionella Urine Antigen Testing (LUAT) on the Local Epidemiology and Diagnosis of Legionella Pneumonia

Overview

There has never been a paper published or research done to determine the rate of Legionella species as a cause of community or nosocomial acquired pneumonia requiring hospitalization in Malaysia. Anecdotally, Legionnaires' disease is thought to be uncommon in Malaysia. This is one of the first prospective hospital-based studies to comprehensively evaluate the epidemiological and demographical factors of patients hospitalized with Legionella infection in Malaysia.

Legionellosis is an environment-related, acute gram negative bacterial respiratory infection and is caused primarily by the species Legionella pneumophila, an atypical pulmonary pathogen, in the likes of mycoplasma and chlamydia species. Potentially all Legionella spp. may cause human disease, however, the majority (92%) of clinical cases are caused by L. pneumophila and the predominant serogroup is serogroup 1. Globally, 1-5% of community acquired pneumonia patients is caused by Legionella spp. and is a challenge to public health authorities. The incidence of Legionella Pneumonia in the US has exceeded expectations and is increasing, with at least 13,000 cases occurring annually. In Singapore, Legionella spp. is responsible for 2-7% of cases of hospitalized community-acquired pneumonia. Legionella pneumophila is being increasingly recognized as a common pathogen causing both community-acquired and nosocomial pneumonia that is responsible for significant morbidity and mortality. It is also one of the most common aetiology discovered when pneumonia is sufficiently severe to require admission to an intensive care unit. It's likely to cause a severe form of pneumonia with high likelihood of adverse medical outcomes which includes rapid deterioration, respiratory failure and the need for intensive care unit (ICU) admission. It will be impossible to distinguish patients with Legionnaires' disease from patients with other types of pneumonia clinically. The key to diagnosis is to perform microbiologic testing when a patient is stratified into a high-risk category. Rapid diagnosis of these pneumonias is desired as delayed diagnosis and institution of appropriate antibiotics is associated with poor outcomes. In routine clinical practice, legionellosis is rarely proven by culture whereas detection of urinary antigen is now common. In US and Europe, case detection rates were revolutionized with the usage of urine antigen test at 97% and 79% respectively. Urine antigen testing has a reported sensitivity that ranges between 76% and 86% for cases of Legionella pneumonia serogroup 1 and a specificity that approaches 100%. In this region, urine antigen test is rarely done due to lack of clinical awareness, a perception that Legionella infection is uncommon and due to the lack of availability of this test regionally. The introduction of the immunochromatographic (ICT) membrane assay to detect antigenuria has revolutionized the usage of UAT to diagnose Legionella infections. The ICT assay is similar to a home pregnancy test and is commercially available. The test is simple to perform and does not require special laboratory equipment, and results can be obtained within 15 minutes. The investigators wish to utilize this innovation to test patients whom are hospitalized with pneumonia and determine the incidence of Legionella infection in the local setting.

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