Outbreak of antiviral drug-resistant influenza a in long-term care facility, Illinois, USA, 2008

Abstract

An outbreak of oseltamivir-resistant influenza A (H1N1) occurred in a long-term care facility. Eight (47%) of 17 and 1 (6%) of 16 residents in 2 wards had oseltamivir-resistant influenza A virus (H1N1) infections. Initial outbreak response included treatment and prophylaxis with oseltamivir. The outbreak abated, likely because of infection control measures.

Figure 1

Number of cases of influenza by date of symptom onset and outbreak control protocol during an influenza A outbreak in a long-term care facility, Illinois, USA, 2008. Retrospective medical chart review of all nontested building A residents identified 1 potential missed case-patient with influenza who had symptom onset on January 29. Additional cases were detected in 2 other residential buildings in the long-term care facility (buildings B and C). Building B housed 53 residents in 4 wards and building C housed 16 residents in 1 ward. All (100%) of residents in both buildings had received the 2007–08 influenza vaccine. Of the 16 rapid test specimens with negative results from all 3 buildings that were subjected to confirmatory testing, 5 (31%) were positive by reverse transcription–PCR for influenza A virus (H1N1).

Figure 2

Phylogenetic analysis of the hemagglutinin gene (HA1 portion) of influenza A viruses (H1N1) isolated during an influenza A outbreak in a long-term care facility, Illinois, USA, 2008. Viruses from buildings A and B shared nearly identical sequences. One of the viruses from building B was more similar in sequence to 1 virus from building A. However, this finding could reflect natural variance in circulating viruses. Red indicates outbreak viruses, boldface italics indicates vaccine strain for 2008–09, boldface indicates vaccine strain for 2007–08, and arrows indicate nucleotide differences in HA1 subunit. Scale bar indicates nucleotide substitutions per site.