Non-typhoidal Salmonella infections among children in a tertiary hospital in Ningbo, Zhejiang, China, 2012-2019

Abstract

Background: Non-typhoidal Salmonella (NTS), a common cause of diarrheal enterocolitis, may also cause severe invasive diseases. Limited information on NTS infections in children is available in China.

Methods: We performed a retrospective study of children admitted to the Ningbo Women and Children's Hospital with culture-confirmed NTS infections between January 2012 and December 2019. Clinical and microbiological information were collected. We compared demographic, clinical and antibiotic resistance variables of invasive NTS (iNTS) infections and non-invasive NTS (non-iNTS) infections, and explored associations between hospitalizations for pediatric NTS infections and temperature and rainfall.

Results: A total of 166 pediatric hospitalizations due to NTS infection were identified during the 8-year study period. Most of the 166 children were <5 years old (93.4%). The primary serotype was Salmonella Typhimurium (62.6%). Of 166 children with NTS infections, 11 had invasive infection. Compared to 155 children with non-iNTS infections, we found that iNTS infections were more likely to occur in infants ≤6 months or children with an underlying medical condition of leukemia at admission, but iNTS infections less often presented with a symptom of diarrhea (P <0.05 in all cases). The resistance rates of non-iNTS isolates to ceftazidime, ceftriaxone, cefepime, and aztreonam were significantly higher than those of iNTS isolates (P <0.05 in all cases). In addition, compared with iNTS isolates, non-iNTS isolates were significantly associated with resistance to ≥4 CLSI (Clinical and Laboratory Standard Institute) classes (P = 0.041, OR: 0.089, 95% CI: 0.009-0.901) and ≥2 first-line treatment agents (P = 0.040, OR: 0.159, 95% CI: 0.028-0.916). On the other hand, we found that seasonal NTS hospitalizations were positively associated with average seasonal temperature (r = 0.961, P = 0.039) and average monthly rainfall (r = 0.921, P <0.001).

Conclusion: Non-iNTS accounts for the majority of infections in this study; infants ≤6 months and children with underlying medical conditions of leukemia are more likely to have invasive infection. The rates of antibiotic resistance in the iNTS isolates are generally lower than those in the non-iNTS isolates. On the other hand, high temperatures and heavy rainfall are positively associated with NTS hospitalizations among children in Ningbo.

Fig 1. Distribution of the 166 NTS infection cases by year of admission and invasiveness.

The bar chart shows the number of NTS infection cases hospitalized in Ningbo in each year from 2012 to 2019, according to the invasive or non-invasive status of infections. Abbreviations: NTS = non-typhoidal Salmonella.

Fig 2. Drug resistance trends (resistant to≥ 4 CLSI classes and ≥2 first-line agents) of 166 Salmonella isolates in Ningbo,2012–2019.

The percentage of resistance (%) over the 8-year study period in Ningbo is shown in the line graph.

Fig 3. Distribution of 166 NTS infection cases and average monthly rainfall in Ningbo, 2012–2019.

The bar chart shows the distribution of the 166 NTS infection cases according to the month of admission. The average monthly rainfall over the 8-year study period in Ningbo is shown in the line graph. Abbreviations: NTS = non-typhoidal Salmonella, Jan = January, Feb = February, Mar = March, Apr = April, Jun = June, Jul = July, Aug = August, Sep = September, Oct = October, Nov = November, Dec = December.

Fig 4. Distribution of the 166 NTS infection cases and average seasonal temperature in Ningbo, 2012–2019.

The bar chart shows the distribution of the 166 NTS infection cases according to the admission. The average seasonal temperature over the 8-year study period in Ningbo is shown in the line graph. Difference in seasonal numbers of NTS infections: P<0.01 vs winter, P<0.001 vs winter, ## P <0.01 vs spring, ### P <0.001 vs spring, Abbreviations: NTS = non-typhoidal Salmonella.