Human monocytotropic ehrlichiosis—A systematic review and analysis of the literature.

Human monocytotropic ehrlichiosis (HME) is a tick-borne bacterial infection caused by Ehrlichia chaffeensis. Most available data come from case reports, case series and retrospective studies, while prospective studies and clinical trials are largely lacking. To obtain a clearer picture of the currently known epidemiologic distribution, clinical and paraclinical presentation, diagnostic aspects, complications, therapeutic aspects, and outcomes of HME, we systematically reviewed the literature and analyzed and summarized the data. Cases of HME are almost exclusively reported from North America. Human infections due to other (non-chaffeensis) Ehrlichia spp. are rare. HME primarily presents as an unspecific febrile illness (95% of the cases), often accompanied by thrombocytopenia (79.1% of the cases), leukopenia (57.8% of the cases), and abnormal liver function tests (68.1% of the cases). Immunocompromized patients are overrepresented among reviewed HME cases (26.7%), which indicates the role of HME as an opportunistic infection. The incidence of complications is higher in immunocompromized compared to immunocompetent cases, with ARDS (34% vs 19.8%), acute renal failure (34% vs 15.8%), multi organ failure (26% vs 14.9%), and secondary hemophagocytic lymphohistiocytosis (26% vs 14.9%) being the most frequent reported. The overall case fatality is 11.6%, with a significant difference between immunocompetent (9.9%) and immunocompromized (16.3%) cases, and sequelae are rare (4.2% in immunocompetent cases, 2.5% in immunocompromised cases). Author summary: Human monocytotropic ehrlichiosis (HME) is a bacterial disease caused by Ehrlichia chaffeensis which is transmitted by tick bites and exclusively reported from Northern America. Infections with other Ehrlichia bacteria are rare, and only very rarely are such cases reported from outside North America. Most cases of HME are likely to be asymptomatic, and symptomatic cases of HME can be easily overlooked or confused as they present primarily as a non-specific febrile illness. Patients with a weakened immune system (e.g. organ transplant patients) are more susceptible to HME and show more complications when compared to patients with a normal immune system. Although response to antimicrobial treatment is usually fast and effective, complications may arise (particularly in patients with a weakened immune system) and the outcome even be fatal. Since most available data on HME comes from case reports, case series and retrospective studies, data on several aspects of the disease remains patchy. To obtain a better overview on various aspect of HME we systematically reviewed the existing literature and compiled and analyzed the reported data on epidemiology, clinical presentation, complications, diagnosis, treatment, and outcome of HME. [ABSTRACT FROM AUTHOR]