A systematic review of the global seasonality of infections caused by Acinetobacter species in hospitalized patients

Background: Acinetobacter is a leading multidrug resistant pathogen in hospitals worldwide that has been seen to exhibit periodic surges during summer months. However, winter peaks and lack of seasonality have also been noted.

Objectives: To systematically collate and examine the evidence describing seasonal patterns in the incidence of Acinetobacter infection in hospitalized patients.

Data sources: MEDLINE/Ovid, EMBASE, Scopus and Web of Science.

Study eligibility criteria: Longitudinal observational studies investigating seasonal variation in the incidence of Acinetobacter infection.

Participants: Patients receiving hospital care.

Interventions: Routine hospital care.

Methods: Systematic review with narrative evidence synthesis structured around clinical and methodological heterogeneity and internal validity of retrieved studies, seasonal patterns and risk factors detected, and stated hypotheses of mechanisms underlying seasonality. To examine consistency in reported seasonal patterns across different conditions, monthly incidence data were extracted, standardised, weighted and presented graphically.

Results: Twenty-five studies reporting 37006 cases of Acinetobacter infection or colonization during 1954 months of follow-up were reviewed. Standardised monthly incidence data pooled across studies exhibited a global seasonal pattern with an incidence peak in summer/warmer months and a trough in winter/colder months. This seasonal pattern remained consistent under different weighting schemes accounting for study size, length of follow-up and overall quality assessment rating. Seasonality persisted in different clinical settings and for different types and sources of infection. Nine studies provided consistent evidence of temperature-associated variation in Acinetobacter incidence, while there were controversial findings regarding other environmental variables. No study detected patient-related or clinical practice-related seasonal variation in Acinetobacter incidence.

Conclusions: Despite substantial clinical and methodological heterogeneity in retrieved studies, a consistent global seasonal pattern in Acinetobacter infection incidence was evident in this review. This merits attention when designing or evaluating infection control interventions in hospitals. Future research should focus on elucidating driving mechanisms underlying the observed seasonality.