Establishing and validating syndromic surveillance of gastrointestinal infections using routine emergency department data, Germany, 2019-2023.

Gastrointestinal infections in Germany account for 24.5 million outpatient visits annually. To enhance outbreak detection and trend monitoring, we developed and validated a syndrome definition for syndromic surveillance of gastrointestinal infections in emergency departments. We selected presenting complaints (Canadian Emergency Department Information System) and diagnoses (ICD-10) to develop the syndrome definition. Validation involved cross-correlation analysis of syndromic and laboratory-based surveillance trends (norovirus-gastroenteritis, rotavirus-gastroenteritis, campylobacteriosis and salmonellosis notifications). We included emergency departments from the German AKTIN registry with continuous data transmission (01/2019-06/2023). Our novel syndrome definition combined complaints (diarrhoea, vomiting, nausea) and diagnoses (intestinal infectious diseases). Across 864,353 visits in 7 emergency departments, 2.1% (n = 18,158) were gastrointestinal infection cases. Of those, 57% (n = 10,424) were female; 23% were aged 0-19 years (n = 4108); and 23% 20-39 years (n = 4116). Trends were similar between surveillance systems. Cross-correlation was 0.73 (95%-confidence interval 0.61-0.85; p < 0.001) at lag - 1, indicating a 1-week relative reporting delay of laboratory-based surveillance. Coherent trends and significant cross-correlation validated our syndrome definition. This novel automated syndromic surveillance complements laboratory-based surveillance while offering improved timeliness and reduced workload. Therefore, it was implemented in Germany's national routine surveillance of emergency departments.