Risk factors associated with long-term shedding infections of non-typhoidal Salmonella in humans

Non-typhoidal Salmonella (NTS) gastroenteritis in humans is typically self-limited, resolving within 48-72 h. However, some infections result in a carrier state characterised by persistent gut colonisation and long-term shedding (LTS). This study aimed to investigate risk factors associated with LTS of NTS in humans.

Salmonellosis cases reported to the Norwegian surveillance system in 2019 were invited to participate. Participants submitted a follow-up stool sample and a questionnaire five weeks after initial sampling (detecting infection). Stool samples were cultured, and isolates were sequenced to determine genotype, serotype and antimicrobial resistance genotype. NTS cases were classified as LTS if the isolates from both samples differed by ≤ 5 alleles. Adjusted odds ratios (aORs) with 95% confidence intervals (95%CIs) were calculated using logistic regression to investigate potential risk factors associated with LTS.

Of 1,094 reported cases, 255 (23%) with NTS participated; 24% were classified as LTS. Children aged 0-5 years were 6.7 times more likely to exhibit LTS compared to adults aged 18-44 years (aOR = 6.71, 95%CI:1.67-26.94). Participants who received regular medication and those following a lactose-free diet were 2.2 (aOR = 2.17, 95%CI:1.02-4.64) and 7.2 (aOR = 7.24, 95%CI:1.48-35.40) times more likely to exhibit LTS than those who did not, respectively. Participants with S. Agbeni or S. Bron were 6 times more likely to exhibit LTS compared to S. Typhimurium cases (aOR = 6.29, 95%CI:1.40-28.16).

Observed risk factors associated with LTS included young age, regular medication use, lactose-free diet, and specific Salmonella serotypes. Further research is needed to increase knowledge regarding LTS and inform infection control measures.