Background
It is a well-known fact, as Lake et al. (2009) report, that "increased ambient temperature may lead to increased foodborne illness for several reasons," and that in the absence of any control measures "increased ambient temperatures may therefore increase bacterial reproduction at various points along the food chain, making the consequences of any subsequent ingestion more severe," citing the studies of Heyndrickx et al. (2002), Tam et al. (2003) and Kovats et al. (2004).

What was done
To gain a better understanding of these coupled phenomena and see how their relationships may have changed over the years, the seven scientists studied food poisoning, campylobacteriosis, salmonellosis, Salmonella Typhimurium infections and Salmonella Enteritidis infections in England and Wales from the mid-1970s and early 1980s to 2007, based on data obtained from the UK's Office for National Statistics and its Health Protection Agency.

What was learned
The work of the United Kingdom researchers revealed that all five of the maladies they studied "were positively associated (P<0.01) with temperature in the current and previous week," and that "food poisoning, salmonellosis and S. Typhimurium infections were also associated with temperature 2-5 weeks previously (P<0.01)," supportive of the view that rising temperatures could indeed lead to increases in these health problems. However, they also found "there were significant reductions in the impact of temperature on foodborne illnesses over time," consistent with "reduced pathogen concentrations in food and improved food hygiene over time."

What it means
Lake et al. note that some prior studies -- Bentham and Langford (2001), Ebi et al. (2006) and McMichael et al. (2006) -- have extrapolated results of the incidence of foodborne illness as a function of temperature into the future, with the result that they portend increases in foodborne illnesses in a warming world. Their results, however, suggest that this tendency can actually be reversed "through reducing the pathogen levels in major food groups and improving food hygiene at the domestic and institutional level," as has successfully been done in England and Wales.

References
Betham, G. and Langford, I.H. 2001. Environmental temperatures and the incidence of food poisoning in England and Wales. International Journal of Biometeorology 45: 22-26.

Ebi, K.L., Mills, D.M., Smith, J.B. and Grambsch, A. 2006. Climate change and human health impacts in the United States: an update on the results of the U.S. National Assessment. Environmental Health Perspectives 114: 1318-1324.

Heyndrickx, M., Vandekerchove, D., Herman, L., Rollier, I., Grijspeerdt, K. and De Zutter, L. 2002. Routes for salmonella contamination of poultry meat: Epidemiological study from hatchery to slaughterhouse. Epidemiology and Infection 129: 253-265.

Kovats, R.S., Edwards, S.J., Hajat, S., Armstrong, B.G., Ebi, K.L., Menne, B. et al. 2004. The effect of temperature on food poisoning: a time-series analysis of salmonellosis in ten European countries. Epidemiology and Infection 132: 443-453.

McMichael, A.J., Woodruff, R.E. and Hales, S. 2006. Climate change and human health: present and future risks. Lancet 367: 859-869.

Tan, C.C., Rodrigues, L.C. and O'Brien, S.J. 2003. The study of infectious intestinal disease in England: what risk factors for presentation to general practice tell us about potential for selection bias in case-control studies of reported cases of diarrhoea. International Journal of Epidemiology 32: 99-105.