Epidemiology and antimicrobial resistance of invasive non-typhoidal Salmonellosis in rural Thailand from 2006-2014

<div><p>Introduction</p><p>Invasive salmonellosis is a common cause of bloodstream infection in Southeast Asia. Limited epidemiologic and antimicrobial resistance data are available from the region.</p><p>Methods</p><p>Blood cultures performed in all 20 hospitals in the northeastern province of Nakhon Phanom (NP) and eastern province of Sa Kaeo (SK), Thailand were captured in a bloodstream infection surveillance system. Cultures were performed as clinically indicated in hospitalized patients; patients with multiple positive cultures had only the first included. Bottles were incubated using the BacT/Alert system (bioMérieux, Thailand) and isolates were identified using standard microbiological techniques; all <i>Salmonella</i> isolates were classified to at least the serogroup level. Antimicrobial resistance was assessed using disk diffusion.</p><p>Results</p><p><i>Salmonella</i> was the fifth most common pathogen identified in 147,535 cultures with 525 cases (211 in Nakhon Phanom (NP) and 314 in Sa Kaeo (SK)). The overall adjusted iNTS incidence rate in NP was 4.0 cases/100,000 person-years (95% CI 3.5–4.5) and in SK 6.4 cases/100,000 person-years (95% CI 5.7–7.1; p = 0.001). The most common serogroups were C (39.4%), D (35.0%) and B (9.9%). Serogroup D predominated in NP (103/211) with 59.2% of this serogroup being <i>Salmonella</i> serovar Enteritidis. Serogroup C predominated in SK (166/314) with 84.3% of this serogroup being <i>Salmonella</i> serovar Choleraesuis. Antibiotic resistance was 68.2% (343/503) for ampicillin, 1.2% (6/482) for ciprofloxacin (or 58.1% (280/482) if both intermediate and resistant phenotypes are considered), 17.0% (87/512) for trimethoprim-sulfamethoxazole, and 12.2% (59/484) for third-generation cephalosporins (cefotaxime or ceftazidime). Multidrug resistance was seen in 99/516 isolates (19.2%).</p><p>Conclusions</p><p>The NTS isolates causing bloodstream infections in rural Thailand are commonly resistant to ampicillin, cefotaxime, and TMP-SMX. Observed differences between NP and SK indicate that serogroup distribution and antibiotic resistance may substantially differ throughout Thailand and the region.</p></div

Age distributions for the major serogroups of invasive non-typhoidal <i>Salmonella</i> in Nakhon Phanom and Sa Kaeo provinces.

<p>Age distributions for the major serogroups of invasive non-typhoidal <i>Salmonella</i> in Nakhon Phanom and Sa Kaeo provinces.</p

Antibiotic resistance among invasive non-typhoidal <i>Salmonella</i> isolates by province and year.

<p>Solid line graph shows number of positive blood cultures and the dashed line indicates the total number of bottles incubated by year (z-axis). TMP-SMX = trimethoprim-sulfamethoxazole.</p

Antimicrobial susceptibility^a profiles for non-typhoidal <i>Salmonella</i> isolates by serogroup and province.

<p>Antimicrobial susceptibility<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006718#t003fn002" target="_blank">^a</a> profiles for non-typhoidal <i>Salmonella</i> isolates by serogroup and province.</p

Epidemiology and antimicrobial resistance of invasive non-typhoidal Salmonellosis in rural Thailand from 2006-2014 - Fig 3

<p><b>Incidence of invasive non-typhoidal Salmonellosis by age group and year in Sa Kaeo (SK, left) and Nakhon Phanom (NP, right) provinces, 2006–2014.</b> RR = relative risk, measured differences between SK and NP. Relative risk is given with upper and lower 95% confidence intervals. * designates age group differences between NP and SK within the specified year (p-value < 0.05) and likely to be driving the differences.</p

Association of discharge diagnosis and serogroup with case outcome among patients with invasive non-typhoidal Salmonellosis.

<p>Association of discharge diagnosis and serogroup with case outcome among patients with invasive non-typhoidal Salmonellosis.</p

Demographic and clinical characteristics of patients with invasive non-typhoidal Salmonellosis in Nakhon Phanom and Sa Kaeo provinces, 2006–2014.

<p>Demographic and clinical characteristics of patients with invasive non-typhoidal Salmonellosis in Nakhon Phanom and Sa Kaeo provinces, 2006–2014.</p

Flow diagram of blood culture data identifying non-typhoidal Salmonella cases, Nakhon Phanom and Sa Kaeo provinces, 2006-2014.

<p>Blood culture bottles were incubated at 35°C for up to 5 and 42 days (F and MB bottles respectively), or until the instrument signaled positive for growth (i.e., positive signal). Culture bottles that did not signal positive after the specified incubation periods (no signal) were considered to be negative without terminal subculture. A. The following organisms were considered likely contaminants and not included in the analysis: S<i>treptococcus viridans</i> group, <i>Corynebacterium</i> spp., <i>Bacillus</i> spp. (other than <i>B</i>. <i>anthracis</i>), <i>Staphylococcus</i> spp. (other than <i>S</i>. <i>aureus</i>), and <i>Aerococcus</i> spp. B. The unknown category were non-identifiable isolates using our standard biochemical testing including Gram-positive and negative cocci (n = 197 and 11 respectively), and Gram-positive bacilli (n = 343); these are likely contaminants. Gram-negative bacilli (n = 12) and unknown other (n = 708). C. The automated blood culture instrument signaled positive, but subculture yielded no organism.</p

Distribution of invasive non-typhoidal Salmonella serovars isolated in two rural Thai provinces between 2006 and 2014.

<p>Distribution of invasive non-typhoidal Salmonella serovars isolated in two rural Thai provinces between 2006 and 2014.</p

Epidemiology and antimicrobial resistance of invasive non-typhoidal Salmonellosis in rural Thailand from 2006-2014 - Fig 4

<p><b>Distribution of non-typhoidal <i>Salmonella</i> serogroups causing invasive infection by year in Nakhon Phanom (top) and Sa Kaeo (bottom), 2006–2014</b>. “Other” includes non-typed <i>Salmonella enterica</i> isolates and isolates from serogroups with few isolates.</p