# Epidemiological pattern and incidence estimation of infectious diarrhea before the COVID-19 pandemic: Beijing, China, 2015–2019

## TL;DR

This study analyzed the causes and patterns of infectious diarrhea in Beijing from 2015 to 2019, identifying norovirus, DEC, and rotavirus as the main pathogens.

## Contribution

The study provides updated incidence estimates and epidemiological patterns of infectious diarrhea in Beijing before the COVID-19 pandemic.

## Key findings

- Norovirus was the most common viral pathogen, followed by rotavirus.
- Diarrheagenic Escherichia coli (DEC) was the most prevalent bacterial pathogen.
- Estimated annual infectious diarrhea cases in Beijing were around 68,054.

## Abstract

To analyze the epidemiological characteristics and estimate the incidence of infectious diarrhea in Beijing, China, 2015–2019.

From January 2015 to December 2019, stool specimens and epidemiological data of diarrhea cases were collected from sentinel hospitals across all districts. Viral pathogens were detected by real time PCR or RT-PCR, including rotavirus, norovirus, astrovirus, adenovirus and sapovirus. Bacterial pathogens were detected using culture, biochemical and serological assays, including Vibrio cholerae, Shigella, Salmonella typhi and Salmonella paratyphi, diarrheagenic Escherichia coli (DEC), non-typhoidal Salmonella (NTS), Vibrio parahaemolyticus, Campylobacter and other bacteria. Descriptive statistics and a Monte Carlo multiplier model were applied for analysis and incidence estimation.

A total of 27,804 outpatients were included from 2015 to 2019. Among cases tested for viral pathogens (N = 9,351), norovirus (1,572/9,351, 16.81%) was the most prevalent, followed by rotavirus (907/9,351, 9.70%). Among those tested for bacterial pathogens (N = 20,741), diarrheagenic Escherichia coli (DEC) (1,941/20,741, 9.36%) was predominant, followed by non-typhoidal Salmonella (NTS) (4.55%) and Vibrio parahaemolyticus (4.17%). Notably, enteroaggregative E. coli (35.65%) was the predominant type of DEC identified in this study. The detection rates of viral pathogens were higher in winter and spring. Rotavirus was mainly identified in cases under 5 years of age, while norovirus was more common in cases aged 18–40 years old. Bacterial pathogens were mainly identified in cases aged 18–40 years old in summer. Estimated by the model, the average annual number of infectious diarrhea cases in Beijing from 2015 to 2019 was approximately 68,054 (95%CI: 49,917–104,149). While the model result indicates the presence of significant hidden burden, but are constrained by inherent limitations in the modeling approach and monitoring design.

Diarrhea remains a serious public health problem in Beijing, China. Norovirus, DEC, and rotavirus were the predominant pathogens among diarrhea outpatients in Beijing. Continuous surveillance is necessary for guiding prevention and control strategies.