Pertusis outbreaks in aged-care facilities.

We concur with Al-Murieb and colleagues that pertussis outbreaks are a potential and probably under-recognised problem in aged-care facilities.1 In February 1999, we investigated an outbreak of acute respiratory infection, which had affected over 50% of the residents of a Sydney nursing home. Serological and virological testing pointed to influenza A as the major cause of illness in 19 of 35 coughing residents.2 However, 10 residents also had evidence of recent pertussis infection based on the presence in serum of IgA antibodies to Bordetella pertussis detected using an in-house, whole-cell antigen assay, which has been shown not to cross-react with sera containing elevated antibody titres to influenza A virus.3 Of these 10 residents, one demonstrated seroconversion to Bordetella IgA on parallel testing of serum samples collected during the outbreak and 7 months earlier.2