Systematic review and meta-analysis of the proportion and associated mortality of polymicrobial (vs monomicrobial) pulmonary and bloodstream infections by Acinetobacter baumannii complex

Background Differentiating Acinetobacter baumannii complex (ABC) infection from colonization remains difficult and further complicated in polymicrobial infections. Purpose To assess the frequency of polymicrobial ABC infections and associated mortality. We hypothesized a lower mortality in polymicrobial infections if ABC isolation reflects colonization in some polymicrobial infections. Methods A systematic review was conducted in PubMed, Scopus and CENTRAL for studies reporting ABC pulmonary and bloodstream infections. The proportion of infections that were polymicrobial and the magnitude of the association between polymicrobial (vs monomicrobial) infection and mortality were estimated with meta-analyses. Results Based on 80 studies (9759 infections) from 23 countries, the pooled proportion of polymicrobial infection was 27% (95% CI 22-31%) and was similarly high for bloodstream and pulmonary infections. Polymicrobial infection was variably and insufficiently defined in most (95%) studies. Considerable heterogeneity (I-2 = 95%) was observed that persisted in subgroup analyses and meta-regressions. Based on 17 studies (2675 infections), polymicrobial infection was associated with lower 28-day mortality (OR = 0.75, 95% CI 0.58-0.98, I-2 = 36%). However, polymicrobial infection was not associated with in-hospital mortality (OR = 0.97, 95% CI 0.69-1.35, I-2 = 0%) based on 14 studies (953 infections). The quality of evidence (GRADE) for the association of polymicrobial (vs monomicrobial) infection with mortality was low and at high risk of bias. Conclusion Polymicrobial ABC infections are common and may be associated with lower 28-day mortality. Considering the heterogeneity of polymicrobial infections and limitations of the available literature, more research is required to clarify the clinical impact of polymicrobial (vs monomicrobial) ABC infection.