Babesiosis causes false-positive HIV test results

It is believed that Babesia may cause false-positive HIV test results, possibly due to Babesia and HIV serologies cross-reacting, according to a new study, “Acute Babesiosis Causing a False-Positive HIV Result: An Unexpected Association,” by He and colleagues.

Investigators describe the case of a patient with acute babesiosis who prior to treatment tested positive for HIV.

The 60-year-old man was admitted to the emergency department with intermittent fever, fatigue, anorexia, and worsening jaundice for three weeks. He was referred by his primary care doctor due to abnormal laboratory values and parasites in the blood.

A blood smear showed Babesia microti with 1-2% infected red blood cells. “Given the patient’s severe presentation but relatively low percentage of infected red blood cells, HIV testing was done,” the authors write.

The fourth-generation HIV 1/2 antigen/antibody test was initially positive but after treatment, HIV testing was negative.

“Our case report adds to the small amount of literature showing that false-positive HIV testing in patients with babesiosis is possible.”

The patient was treated for Babesia with atovaquone and azithromycin and doxycycline to cover other possible tick-borne diseases.

“An exchange transfusion was performed due to the patient’s severe presentation,” according to the authors.

The patient’s symptoms resolved following treatment. And repeat testing for HIV was negative.

“False-positive fourth-generation HIV tests are rare,” the authors point out. However, a few case reports “have described false-positive HIV tests associated with acute babesiosis.”

The authors conclude:

• “While the reasons for false-positive HIV tests in acute babesiosis remain unclear, physicians who see patients with a positive HIV test in the setting of acute babesiosis should pursue further workup.”