The Impact of Legionella Urine Antigen Testing (LUAT) on the Local Epidemiology and Diagnosis of Legionella Pneumonia - A Hospital Based Study 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%.