Salmonellosis in North Thames (East), UK: associated risk factors

Abstract

We assessed the rate of salmonella infections and risk factors associated with infection in North East Thames in 1993. Cases of culture confirmed infection were identified through microbiology laboratories and environmental health officers in the North East Thames. A total of 1730 cases were reported and 209 of these individuals (those who could be contacted within a 3-week interval after onset of symptoms) and matched controls were interviewed by telephone. In addition randomly selected controls were interviewed over a 4-month period about recent gastric acid lowering medication and antimicrobial ingestion. Sixty-six serotypes were identified: S. enteritidis was isolated from 1179 (69%) cases, S. typhimurium from 221 (13%), S. virchow from 77 (4%) and S. newport 25 (1%). Infections were more frequent in summer months. Highest rates were documented in children under 2 years of age for S. enteritidis (108/100000) and under 1 year for S. typhimurium (36/100000). Using the Townsend score, highest isolation rates of S. enteritidis were in more prosperous areas (36/100000 vs. 27/100000; odds ratio (OR) 1·3, 95% confidence intervals (CIs) 1·2–1·6, P<0·0001), while for S. typhimurium, there was no relation between deprivation index and isolation rates areas (6·4/100000 vs. 6·1/100000; OR 1·1, 95% CIs 0·8–1·5, P=0·77). The case control study showed a significant association between ingestion of products containing raw eggs and S. enteritidis infection (8/111 cases vs. 0/110 controls; OR undefined, lower 95% CIs 3·4). Individuals with salmonella infection were significantly more likely to have travelled abroad in the week before the onset of illness [42/186 (23%) vs. 1/182 (0·5%) ; OR 40, 95% CIs=5·5–291, P<0·001] and to report gastroduodenal disease [11/143 (7 %) vs. 3/143 (2 %); OR 5·0, 95% CIs=1·1–23, P=0·04]. There was an association between illness and gastric acid-lowering medications [unmatched controls OR 22·3 (95% CIs 1·5–3·7, P=0·0002), matched controls OR 3·7 (95% CIs 1·0–3·8, P=0·07)], but no association with antimicrobial ingestion.