In August 2019, a 75-year-old man presented to the emergency department in Winnipeg with a 6-week history of fever, myalgia, lethargy and 7-kg weight loss. After 3 weeks of symptoms, he had visited his family physician, who prescribed a 1-week course of amoxicillin-clavulanic acid. When the symptoms persisted despite antibiotic treatment, he went to a community emergency department, where the physician identified anemia and thrombocytopenia (Table 1). After this, an urgent outpatient computed tomography (CT) scan of his chest, abdomen and pelvis was unremarkable. The patient later presented to our emergency department with persistent symptoms, and we admitted him for further investigations.
The patient recalled first feeling ill while boating at Pelican Lake in Ninette, Manitoba, at which time he noticed a new, red, thumb-sized lesion on his right leg. He did not remember finding any ticks or other skin lesions on his body. His travel history was notable for a visit to Arizona 6 months before symptom onset, but he had not been outside North America. Eleven weeks before symptom onset, he had camped at Birds Hill Provincial Park in Manitoba. Seven weeks before his symptoms started, he had visited Burlington, Ontario (Figure 1). He had donated blood 7 weeks before presentation.
On admission to hospital, the patient was febrile (38.6[degrees]C) and tachycardic (105 beats/min). His physical examination was unremarkable, with no insect bites, rashes, lymphadenopathy, hepatosplenomegaly, or jaundice. Given his recent negative CT scan and nonspecific symptoms, the likely cause was infectious, and our differential diagnosis focused on viral and atypical infections.
Investigations showed that the patient's pancytopenia had progressed since his last emergency department visit, and his liver enzyme levels were elevated. Laboratory investigations presented in Table 1 showed evidence of hemolysis and acute kidney injury. Blood culture, urine culture and serology tests for hepatitis A, B and C; HIV; cytomegalovirus; Epstein-Barr virus; West Nile virus; and Borrelia burgdorferi were negative. We did not test for anaplasmosis at the time. His chest radiograph was unremarkable.
To further investigate the patient's anemia and thrombocytopenia, we ordered a peripheral blood smear to rule out microangiopathic hemolytic anemia, which showed intraerythrocytic forms suggestive of malaria. We then ordered thick and thin smears. The initial parasite load was 0.2%, which subsequently peaked at 0.8%. With the patient's history suggestive of an insect bite and no reported travel to a malaria-endemic region, we suspected babesiosis and started empiric treatment with atovaquone and azithromycin. The patient became afebrile by treatment day 3.
A hematopathologist's further analysis of the peripheral smear supported a diagnosis of babesiosis (Figure 2 and Figure 3), and the infectious cause was ultimately confirmed as Babesia microti by polymerase chain reaction (PCR) test. The patient's parasitemia was reduced to 0.1% at the time of his discharge 5 days after admission and 0% 1 week after discharge. His renal function continued to improve, and his pancytopenia and liver enzyme abnormalities resolved (Table 1).
We contacted Canadian Blood Services, which tested the patient's donated blood using PCR, and found it to be...