Outbreak of viral respiratory infections in an aged care facility in NSW - lessons about a pandemic virus

Influenza in aged care facilities (ACFs) is associated with an increased risk of poor health outcomes among residents, including death. In this paper we share our experience of managing an outbreak of viral respiratory infection in an ACF very early in the 2009 influenza pandemic and also describe some of the emerging issues relating to crossreacting antibodies to the pandemic (H1N1) 2009 influenza virus in the very elderly. The outbreak investigation was conducted as part of an urgent public health intervention initiated by the New South Wales (NSW) Department of Health during the early stages of the first southern hemisphere wave of the 2009 pandemic. Nose and throat swabs for nucleic acid testing (NAT) plus acute and convalescent serum samples (6 weeks apart) were collected from all the residents of an ACF where an influenza-like illness (ILI) outbreak occurred. The investigation revealed dual outbreaks of pandemic (H1N1) 2009 influenza and rhinovirus infection. Out of 28 residents, three had laboratory confirmed influenza [two with pandemic (H1N1) 2009], and 10 had rhinovirus infection on NAT. Testing of acute sera collected from every subject found elevated (>= 1:40) pandemic (H1N1) 2009 HAI antibody in 60% (9/15) subjects aged 85 years or more (born before 1925 and median age 88 years; Geometric Mean Titre-GMT 48 1) compared with none of the 13 residents aged under 85 years (born after 1924 and median age 79 years; GMT 10 1, P = 0 01). The ACF was closed to visi-tors for 7 days. The symptomatic residents received treatment-dose oseltamivir, and all other residents were given oseltamivir prophylaxis. More than one virus may be circulating in an ACF with an ILI outbreak at any one time in winter. A significant proportion of elderly residents had pre-existing cross reacting antibody to the pandemic (H1N1) 2009, which may explain the minimal clinical impact of pandemic (H1N1) 2009 in this elderly population.