Risk factors for hospitalization, severe infection, and prolonged disease in patients with babesiosis in the upper Midwest.

Background:

Babesiosis is an emerging parasitic tick-borne disease. Severity of infection can range from asymptomatic to fatal and, though most infections are self-limited or cured with a short course of antibiotics, some patients have prolonged illness despite antimicrobial therapy. Early prognostic indicators to guide clinical decisions and antimicrobial prescribing are needed.

Methods:

A retrospective chart review of patients diagnosed with babesiosis by PCR or smear from 1999-2015 at Marshfield Clinic Health System in northern Wisconsin was completed. Univariate and multivariate analyses were completed and relative risk ratios (RR) with 95% confidence intervals were determined for symptoms, laboratory studies, clinical outcomes, and treatment associated with hospitalization, severe infections, and prolonged disease.

Results:

128 cases of babesiosis were detected. 81(63%) patients were hospitalized, 26(20%) had severe infection, and 11(8.6%) required >14 days of antibiotics. There were no fatalities. Coinfection with Lyme disease, erhlichiosis, or anaplasmosis reduced risk of hospitalization (RR 0.73 CI 0.53-0.99, p=0.03) and did not change risk for severe infection (RR 1.08 CI 0.53-2.18, p=0.84) or prolonged disease (RR1.3 CI 0.66-2.58, p=0.45). Initiation of antibiotic treatment for babesiosis was delayed in patients without coinfection (23.3 vs 17.3 days, p<0.01). Asplenia, nausea or vomiting, diarrhea, urinary changes and total bilirubin >1.9 were associated with need for hospitalization, severe infection, and persistent disease (all p ≤ 0.03). Age >75 years (RR 1.44 CI 1.14-1.82, p=0.01) and underlying cardiac disease (RR1.40 CI 1.09-1.41, p=0.01) were associated with hospitalization. Treatment delay of greater than 7 days after symptom onset increased risk for severe infection (RR2.35 CI 1.01-5.48, p=0.03).

Conclusion: Significant risk factors for development of severe babesiosis included delay in diagnosis and initiation of therapy. Asplenia, nausea or vomiting, diarrhea, urinary changes and elevated bilirubin were also associated with need for hospitalization and prolonged disease treatment. Contrary to prior studies, coinfection with other tick- borne pathogens reduced risk for hospitalization, possibly from earlier recognition of disease.