Babesiosis Acquired through Blood Transfusion, Califor nia, USA Van Ngo and Rachel Civen Babesiosis was reported in a California resident who received a transfusion of blood products collected in the disease-endemic northeastern region of the United States. Babesiosis should be considered year-round in the diagno- sis of febrile and afebrile patients with abnormal blood cell counts who have received blood products from disease- endemic areas. Bcaused by various species of the protozoan genus abesiosis is an infection of red blood cells (RBCs) Babesia. Most human infections reported in the United States are attributed to B. microti and occur most frequently in the Northeast and less commonly in the Midwest (1). Infrequently, babesiosis cases have been documented in California and Washington; however, these cases were caused by local Babesia-like isolates, including B. duncani and a B. divergens–like parasite (1–3). B. microti infection is often asymptomatic but can potentially be severe and even fatal, especially in the elderly, asplenics, and other immunosuppressed persons. Symptoms can be nonspeciﬁc, mimicking many systemic infectious diseases, and include fever, chills, myalgias, fatigue, and jaundice caused by hemolytic anemia (1). Babesiosis is transmitted primarily through the bite of an infected tick, typically Ixodes spp., although occasion- ally transmission occurs via transfusion of blood products collected from asymptomatic infected donors (1). More than 50 transfusion-related cases have been reported in the United States (4). This report describes a transfusion-ac- quired case of babesiosis caused by B. microti in a resident of Los Angeles County, California. The Case On February 12, 2007, a 58-year-old man with meta- static esophageal cancer was admitted to an acute care fa- cility for evaluation of hematemesis and normocytic ane- mia. The initial examination showed he had hypotension without fever, joint swelling, headaches, or rash. Labora- tory evaluation showed a hemoglobin concentration of 8.4 Author afﬁliation: Los Angeles County Department of Public Health, Los Angeles, CA, USA DOI: 10.3201/eid1505.081562 mg/dL, a platelet count of 71,000/mm3, and a leukocyte count of 3.5 × 103/mm3 with 19% bands. Results of liver function tests showed mild elevations in levels of aspartate transaminase (202 mg/dL), alanine transaminase (33 mg/ dL), and total bilirubin (0.7 mg/dL). An abnormal blood cell count prompted a manual dif- ferential count. Babesia spp. was identiﬁed on a periph- eral smear and subsequently conﬁrmed at the Los Angeles County Public Health Laboratory. The result of PCR anal- ysis performed by a commercial laboratory was positive and highly speciﬁc for B. microti DNA, a result conﬁrmed by the Centers for Disease Control and Prevention (CDC) (Table). The commercial laboratory also performed indi- rect ﬂuorescent antibody (IFA) testing for B. microti and found both acute and convalescent specimens to be nega- tive. Conﬁrmatory testing at CDC corroborated the nega- tive result for the acute specimen but showed the convales- cent specimen, collected 8 days after onset, to be positive for B. microti, with a total antibody titer of 64. The patient was treated with azithromycin and atovaquone for 7 days, given 2 blood transfusions for anemia, and discharged in stable condition on February 16, 2007. Before admission, the patient had visited an oncology clinic numerous times for treatment related to his esopha- geal cancer: radiation therapy in October 2006, 3 che- motherapy courses from October 2006 through February 2007, and blood transfusions in January 2007. The patient received 6 units of packed red blood cells (PRBCs) and 2 units of fresh frozen plasma (FFP) over several clinic visits on January 1 and January 22–24, 2007. The patient was in Salt Lake City, Utah, from Janu- ary 13 through January 20, 2007; however, because of poor health, he did not engage in any outdoor activities. At least a year before his admission in 2006, the patient visited an undeveloped property near Klamath Falls, Oregon, where he spent time outdoors. He could not recall ever incurring a tick bite, seeing ticks, or having any animal contact. The Table summarizes the serologic and PCR results for specimens collected from the patient and 6 PRBC do- nors. The PRBC units came from 2 blood banks: 1 in Maine (2 units) and 1 in California (4 units). A blood donor from Maine tested positive for B. microti by IFA, with a total antibody titer 256, but tested negative B. microti by PCR. Testing of specimens from remaining PRBC donors yield- ed negative results. Specimens from FFP donors were not tested because of the low risk for Babesia spp. transmission associated with plasma products. The implicated donor was a 49-year-old male resident of Maine, where babesiosis is less common than in other states in the northeast. For example, whereas Maine typi- cally reports <12 cases annually, Rhode Island has reported up to 61 cases (5,6). However, the donor resided in the southern coastal region of the state, where Maine’s cases Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 15, No. 5, May 2009 785