Legionellosis is a serious pneumonia caused by bacteria of the genus Legionella assigned to the family Legionellaceae. This family now includes 48 species and over 60 serogroups. Approximately 20 species are implicated in human disease. The overwhelming majority of Legionella infections are caused by Legionella pneumophila. Legionnaires' disease is the major clinical manifestation of Legionella infection although extra-pulmonary infection and non-pneumonic disease like Pontiac fever occur.

L. pneumophila is responsible for approximately 90% of legionellosis cases, and of these, over 80% are due to a single serogroup 1.

Diagnosis of legionellosis can be difficult because signs and symptoms are non-specific and do not allow to distinguish L. pneumophila infections from other common causes of pneumonia. L. pneumophila infections are considered to be fairly common but they are probably under-diagnosed and under-reported. 

The detection of antigen in urine has become the most commonly used method for diagnosis of L. pneumophila serogroup 1 because of its high sensitivity and specificity.

 The Legionella V-TesT detects soluble antigen from L. pneumophila serogroup 1 in urine samples.