Changes in the Distribution of Pathogens Causing Meningoencephalitis Before and During the COVID-19 Pandemic.

Background: Infectious meningoencephalitis (ME) is a major global health concern. Viruses are the most frequently implicated etiologies, whereas bacterial causes, although life-threatening, constitute a lesser proportion of ME cases, together with other pathogens. The strict implementation of COVID-19 mitigation measures led to the decreased viral and non-viral infectious diseases. Therefore, this study aimed to investigate the effect of these mea-sures on ME-causing pathogens by age groups.

Methods: This retrospective study aimed to determine and compare the rates of pathogen-positive ME cases during the pre-pandemic (P-1) and pandemic (P-2) periods. Molecular diagnostic methods using the cerebrospinal fluid of patients from all age groups were included. The positivity rate difference of the ME-causing pathogens between the two study periods was compared and the distribution pattern of the pathogens among the age groups was determined.

Results: The overall positivity rate for at least one ME-causing pathogen during P-1 was 22.0% (503/2,284), which significantly declined to 7.3% (83/1,141) during P-2 (p < 0.001). Particularly, a statistically significant decline in the pathogen positivity was observed in the groups 4 - 6 (≥ 3 years) (p < 0.001, p < 0.001, and p = 0.041, respectively). Specifically, the enterovirus cases decreased significantly, whereas the varicella zoster virus and herpes simplex virus-2 cases increased. Among bacterial causes, the S. agalactiae, S. pneumoniae, and E. coli K1 ME cases significantly increased. Men and women had no significant differences in the positivity rate during either study period.

Conclusions: COVID-19 mitigation measures significantly impacted the positivity rates and the distribution of ME-causing agents, especially in the age groups ≥ 3 years, although not uniformly.