The investigators plan to recruit 2,000 cases of community acquired pneumonia (CAP) and 2,000 cases of faecal peritonitis (FP) from 30 UK ICUs and HDUs (members of the UK Critical Care Genomics group − UKCCG). The large number of patients is required to satisfy the power calculations based upon the predicted allele frequencies of candidate genes and the level of functional expression of the gene polymorphisms.