Investigation of Pontiac-like illness in office workers during an outbreak of Legionnaires' disease, 2008.

In July 2008, office workers in Dublin complained of influenza-like illness preceding and interspersing two cases of notified Legionnaires' disease. Legionella pneumophila serogroup 1 was identified in both cooling towers supplying the office. A retrospective cohort study was undertaken to investigate possible Pontiac fever (PF). Forty-seven employees (23%) met the clinical case definition for PF but confirmatory testing was negative. Exposure to the smoking area situated beside the cooling towers was associated with an increased risk of PF (RR 2.4, 95% CI 1.5-3.8). The diagnosis of PF should be considered when many persons exposed to a possible reservoir of Legionella spp. present with flu-like symptoms. More sensitive microbiological tests would allow better confirmation and more comprehensive reporting of PF. Early detection is vital to prevent potentially severe illness and outbreaks of PF or Legionnaires' disease.