Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:5% Cronobacter contamination of PIF in Malaysia was almost in agreement with reports of Cawthorn et al. (2008) and Witthuhn et al. (2006) who found the prevalence of Cronobacter in South African PIF were 14 and 18%, respectively. Muytjens et al. (1988) also reported that 14% of PIF samples were positive for Cronobacter contamination.
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