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Source of rare Salmonella cases in China remains unknown

Scientists have been unable to find the source of a rare type of Salmonella that affected some people in China.

Two children with diarrhea visited a healthcare facility within 24 hours in August 2023. Salmonella Grumpensis was detected in stool samples by a public health laboratory in Shanghai.

According to the study published in China CDC Weekly, the local Chinese Salmonella genome database contained no recorded instances of the serotype, suggesting it is an infrequent occurrence.

Scientists say that discovering two instances of this unusual serotype within 24 hours signals a red flag for a possible outbreak and underscores the pathogen’s transmission capability.

Two young boys, aged 1 and 2 years old, went to the hospital in August with similar clinical symptoms of bloody diarrhea and abdominal pain.

A gap in understanding
Initial findings showed no evidence of typical sources of infection such as dining out, travel, contact with symptomatic individuals, consumption of raw water, undercooked foods, or owning pets. The epidemiological investigation did not yield a probable source due to limited data, but the possibility of a shared infection was deemed feasible.

Laboratory personnel collected specimens from the household of one case. They included stool from family members, uneaten food, and environmental swabs. No Salmonella was detected.

Whole genome sequencing results suggested a strong genetic similarity of both isolates, pointing to a common source.

Analysis of 51 Salmonella Grumpensis genomes in the NCBI database revealed it had been found in 11 countries, with the highest numbers being Spain, the United Kingdom, and the United States. Strains were isolated between 2005 and 2023, and sample types included humans, food, plants, and poultry.

“The limited availability of information on Salmonella Grumpensis globally highlights a gap in understanding its sources and transmission patterns. This serotype has been prevalent in 11 countries and regions globally since 2005, with sources ranging from animal products to plant-based items like chili powders,” said scientists.

“This study highlights the crucial contribution of public health laboratories in identifying and addressing outbreaks of uncommon Salmonella serotypes. It underscores the common dilemma public health departments face in confirming outbreaks that exhibit typical characteristics but are challenging to confirm through regular surveillance due to few cases or unidentified sources.”

Prevalence and diversity of pathogens in Beijing
Researchers examined 1,011 stool samples from suspected foodborne illness cases in another study and found 35 pathogens. The analysis indicated a significant presence of Clostridium perfringens, Salmonella, enterotoxigenic E. coli (ETEC), and adenovirus. Also, co-infections were identified in 720 samples.

From January 2022 to April 2023, scientists studied stool specimens from patients diagnosed with foodborne diseases in 28 hospitals across Beijing.

Clostridium perfringens had the highest positivity rate at 52 percent among the samples analyzed, followed by Salmonella, ETEC, and adenovirus. Enteropathogenic E. coli (EPEC) and enteroaggregative E. coli (EAEC) were also prevalent.

Pathogens found in 5 percent to 15 percent of samples included Staphylococcus aureus, Campylobacter jejuni, rotavirus, Vibrio parahaemolyticus, Shigella/Enteroinvasive E. coli (EIEC), Cronobacter, Aeromonas spp., norovirus, and Vibrio cholera.

Of the co-infections, most involved one, two, or three pathogens, with rare cases having up to nine pathogens detected.

Researchers said while detecting Clostridium perfringens is of interest, it does not suggest a pathogenic role in each instance.

“This finding highlights the critical need to differentiate between true pathogens and commensal organisms within the gastrointestinal tract, offering insights for future efforts to identify bona fide pathogens.”

Scientists plan to extend sample collection efforts and conduct assessments between culture-independent diagnostic test (CIDT) results and traditional culture methods.

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