There have been very few studies comparing the microbiological safety of organic and conventional food production. In theory, organic food could be more prone to microbial contamination due to the lack of preservatives and the use of animal waste or manure as fertilisers are more commonly referred to. However, the results of the present studies have not been conclusive due to a number of factors, including a small sample size and a failure to take into account seasonal and regional variations. Clearly, organic and conventional foods are susceptible to contamination by pathogenic microorganisms at every point in the food chain. It can occur during production from manure and water, during processing from environmental sources and during the final handling and packing, possibly as a result of poor human sanitation. One area where organic production systems might pose a higher risk is through the use of newer untreated manure as fertiliser. Studies carried out on organic and conventional produce found that E. coli contamination was 19 times greater on organic farms that used manure or compost less than 12 months old than on farms that used older materials. Though the risks are reduced as manure matures, researchers have found that many pathogenic organisms such as E. coli and salmonella can still survive up to 60 days or more in compost and in the soil, depending on temperature and the condition of the soil.