Influenza-associated bacterial pathogens in patients with 2009 influenza A (H1N1) infection: impact of community-associated methicillin-resistant Staphylococcus aureus in Queensland, Australia

Abstract

Background: Secondary bacterial pneumonia due to community onset methicillin-resistant Staphylococcus aureus (MRSA) has become a highly publicised cause of influenza-associated death. There is a risk that case reports of fatal outcomes with post-influenza MRSA pneumonia may unduly influence antibiotic prescribing. Aims: The aim of this study was to demonstrate the incidence of community-onset MRSA pneumonia in 2009 H1N1 influenza patients. Methods: The microbiology records of patients positive for influenza A (H1N1) in 2009 were reviewed for positive blood or respiratory tract cultures and urinary pneumococcal antigen results within a Queensland database. Patients with such positive results within 48 h of hospital admission and a positive H1N1 influenza result in the prior 6 weeks were included. Results: In 2009, 4491 laboratory-confirmed pandemic influenza A (H1N1) infections were detected. Fifty patients (1.1% of the H1N1 cohort) who were hospitalised with H1N1 and who had a bacterial respiratory tract pathogen were identified. Streptococcus pneumoniae (16 patients; 32%), Staphylococcus aureus (13 patients; 26%) and Haemophilus influenzae (9 patients; 18%) were the most commonly cultured organisms. Of the cohort of 4491 patients, MRSA was detected in only two patients, both of whom were admitted to intensive care units and survived after prolonged admissions. Conclusions: Influenza-associated community-onset MRSA pneumonia was infrequently identified in the 2009 H1N1 season in Queensland, despite community-onset MRSA skin and soft tissue infections being very common. Although post-influenza MRSA pneumonia is of great concern, its influence on empiric-prescribing guidelines should take into account its incidence relative to other secondary bacterial pathogens.