Legionella pneumonia due to non-Legionella pneumophila serogroup 1: usefulness of the six-point scoring system

Background: Because of a limited number of reports, we aimed to investigate the clinical characteristics of patients with Legionella pneumonia due to non-Legionella pneumophila serogroup 1 and the diagnostic usefulness of the six-point scoring system for such patients compared with patients with pneumonia caused by L. pneumophila serogroup 1.

Methods: We retrospectively analysed patients diagnosed with Legionella pneumonia due to non-L. pneumophila serogroup 1 between March 2001 and June 2016. We examined the clinical characteristics, including symptoms, laboratory findings, radiologic findings, pneumonia severity, initial treatment and prognosis. We also calculated scores using the six-point scoring system in these patients. Furthermore, we compared the clinical characteristics and six-point scores between non-L. pneumophila serogroup 1 patients and L. pneumophila serogroup 1 patients among hospitalized community-acquired pneumonia patients enrolled prospectively between October 2010 and July 2016.

Results: Eleven patients had pneumonia due to non-L. pneumophila serogroup 1; their median age was 66 years and 8 patients (72.7%) were male. The most common pathogen was L. pneumophila serogroup 3 (6/11), followed by L. pneumophila serogroup 9 (3/11), L. pneumophila serogroup 6 (1/11) and L. longbeachae (1/11). Non-specific symptoms, such as fever and cough, were common. Six patients (54.5%) had liver enzyme elevation, but no patient developed hyponatraemia at <130 mEq/L. Nine patients (81.8%) showed lobar pneumonia and 7 patients (63.6%) manifested with consolidation and ground-glass opacity. Patients with mild to moderate severity comprised 10 (90.9%) by CURB-65 and 5 (45.5%) by the Pneumonia Severity Index. Of all patients, 4 were admitted to the intensive care unit and 3 died despite appropriate empiric therapy. The clinical characteristics were not significantly different between non-L. pneumophila serogroup 1 patients and L. pneumophila serogroup 1 patients (n = 23). At a cut-off value of ≥ 2 points, the sensitivity of the six-point scoring system was 54.5% (6/11) for non-L. pneumophila serogroup 1 patients and 95.7% (22/23) for L. pneumophila serogroup 1 patients.

Conclusions: Cases of non-L. pneumophila serogroup 1 pneumonia varied in severity from mild to severe and the clinical characteristics were often non-specific. The six-point scoring system was not useful in predicting such Legionella pneumonia cases.