Clinical Features, Antimicrobial Resistance, and Serogroups of Nontyphoidal Salmonella Isolated From Infants Less Than 3 Months Old in the Recent Decade

Background: Antibiotic treatment is indicated for infants with nontyphoidal Salmonella (NTS) enterocolitis. However, whether antimicrobial resistance (AMR) is a problem among young infants is unknown. This study investigated the characteristics of NTS infections in young infants. Methods: Infants less than 3 months old with NTS infections were enrolled and grouped into 2 cohorts (diagnosed 2010-2015 or 2016-2021). Salmonella isolated from blood or cerebrospinal fluid was defined as invasive NTS (iNTS). The clinical features, AMR and serogroups were compared between cohorts. Results: In total, 102 young infants had NTS infections, 6.9% of which were iNTS. Infants with iNTS infections were younger, hospitalized longer, and received longer antibiotic courses. More than half of cases of iNTS were resistant to ciprofloxacin, ceftriaxone and greater than or equal to 3 antibiotics. iNTS was mainly observed in Salmonella groups C2 and E. Over the past decade, group B (44%), group E (26%) and group C2 (16%) have been the most common serogroups. NTS significantly increased AMR to ciprofloxacin, ceftriaxone and trimethoprim-sulfamethoxazole, and greater than or equal to 3 antibiotics. Both multidrug resistance and extensive drug resistance in NTS also significantly increased. Conclusions: The serogroups varied with time, and the main causes of iNTS, groups C2 and E, increased over the past decade. The prevalence of AMR also increased, especially for iNTS. Given the low iNTS rate and high AMR, routine antibiotic use among infants with NTS infections between 1 and 3 months old should be reconsidered. Further large-scale research is required to formulate therapeutic strategies.