Municipal Wastewater Surveillance Revealed a High Community Disease Burden of a Rarely Reported and Possibly Subclinical Salmonella enterica Serovar Derby Strain

• Published in: Applied and environmental microbiology 2020-08, Vol.86 (17)
• Main Authors: Diemert, Sabrina, Yan, Tao
• Format: Article
• Language: English
• Subjects: Asymptomatic; Colonization; Epidemiological Monitoring; Gastroenteritis; Gene sequencing; Genes; Genomes; Hawaii - epidemiology; Health surveillance; Humans; Immune response; Infections; Infectious diseases; Monitoring; Municipal wastewater; Pathogenicity; Pathogens; Public and Environmental Health Microbiology; Salmonella; Salmonella enterica; Salmonella enterica - isolation & purification; Salmonella Infections - epidemiology; Salmonella Infections - microbiology; Salmonellosis; Sampling; Serogroup; Subclinical infection; Telemedicine; Virulence; Virulence factors; Waste Water - microbiology; Wastewater; Whole genome sequencing
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.00814-20

Clinical surveillance of enteric pathogens like is integral to track outbreaks and endemic disease trends. However, clinic-centered disease monitoring biases toward detection of severe cases and underestimates the incidence of self-limiting gastroenteritis and asymptomatic strains. Monitoring pathogen loads and diversity in municipal wastewater (MW) can provide insight into asymptomatic or subclinical infections which are not reflected in clinical cases. Subclinical infection patterns may explain the unusual observation from a year-long sampling campaign in Hawaii: serovar Derby was the most abundant pulsotype in MW but was detected infrequently in clinics over the sampling period. Using whole-genome sequencing data of isolates from MW and public databases, we demonstrate that the Derby serovar has lower virulence potential than other clinical serovars, particularly based on its reduced profile of genes linked with immune evasion and symptom production, suggesting its potential as a subclinical salmonellosis agent. Furthermore, MW had high abundance of a rare Derby sequence type (ST), ST-72 (rather than the more common ST-40). ST-72 isolates had higher frequencies of fimbrial adherence genes than ST-40 isolates; these are key virulence factors involved in colonization and persistence of infections. However, ST-72 isolates lack the Derby-specific pathogenicity island 23 (SPI-23), which invokes host immune responses. In combination, ST-72's genetic features may lead to appreciable infection rates without obvious symptom production, allowing for subclinical persistence in the community. This study demonstrated wastewater's capability to provide community infectious disease information-such as background infection rates of subclinical enteric illness-which is otherwise inaccessible through clinical approaches. Wastewater-based epidemiology (WBE) has been conventionally used to analyze community health via the detection of chemicals, such as legal and illicit drugs; however, municipal wastewater contains microbiological determinants of health and disease as well, including enteric pathogens. Here, we demonstrate that WBE can be used to examine subclinical community salmonellosis patterns. Derby was the most abundant serovar detected in Hawaii wastewater over a year-long sampling study, with few corresponding clinical cases. Comparative genomics analyses indicate that the normally rare strain of Derby found in wastewater has a unique combination of genes which a