Trends in pathogens causing bacteraemia in England between 2004 -2008: the emerging importance of Gram negatives

Background: The Health Protection Agency has operated a voluntary system for the surveillance of micro-organisms causing bacteraemia since the 1970s that provides important data for measuring trends in  pathogens and detecting important changes in epidemiology that require public health action

Objective: To determine the trends in pathogens reported by laboratories in England as causing bacteraemia between 2004 and 2008

Methods: Data were extracted from a subset of laboratories with consistent data reporting systems in order to minimise the effects of changes in case ascertainment over time.  Trends were evaluated using a generalised linear model with binomial errors and a log link function for comparing proportions

Results: Bacteraemia in England occurred at a rate of 189 episodes per 100 000 population/year.  In 80% of episodes the cultures were taken in hospitalised patients, in more than half the patients were over 65 years of age, and 54% of episodes occurred in males.  361 263 episodes of bacteraemia were reported by 137 consistently-reporting laboratories between 2004 and 2008.  In these data, reports of E. coli increased by 32% (p <0.001).  E.coli is now the most common cause of bacteraemia in England, accounting for 23% of all bacteraemia reported and more than 30% in those aged over 75 years.  There also were significant increases in bacteraemias caused by other Gram-negative pathogens during this period: Klebsiella spp. (14%), Pseudomonas spp.(24%) and Proteus spp (18%).  Whilst Staphylococcus aureus had previously been the most common reported cause of bacteraemia, the number of episodes declined by 24% between 2006 and 08 (p<0.001).  However, this decrease was only associated with meticillin-resistant strains and episodes caused by meticillin-sensitive S. aureus remained stable between 2004 and 2006, and subsequently increased (p<0.001).  This suggest the affect of national strategies directed at preventing MRSA bacteraemia have not had the same impact on MSSA. Reports of coagulase negative staphylococci bacteraemia have declined significantly since 2007, possibly in association with national guidance aimed at improving blood culture taking practice.

Conclusions: The growth of Gram-negative pathogens as major causes of bacteraemia in England is of particular concern since these organisms are associated with both a high morbidity and increasing resistance to antimicrobial agents.  Some of these bacteraemias may represent community-acquired infections, but most are likely to be associated with healthcare delivered in both hospital and community settings. Further investigation of their underlying cause and strategies for their prevention is an important public health priority.