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In 2012, 22 states conducted surveillance for babesiosis: Alabama, California, Connecticut, Delaware, Indiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Nebraska, New Hampshire, New Jersey, New York, North Dakota, Oregon, Rhode Island, Tennessee, Vermont, Washington, Wisconsin, and Wyoming.

For 2012, among these 22 states where babesiosis is reportable, CDC was notified of 911 cases of babesiosis.

Babesiosis became a nationally notifiable condition in January 2011, which means that CDC is notified of the number of cases that meet the case definition from those health departments where babesiosis is reportable. Surveillance data for 2011 were summarized in an MMWR article. Data for 2012 are summarized below.

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In 2012, the 911 cases were reported in residents of 14 of the 22 states (Figure 1). The other 8 states reported no cases.

Most (96%) of the cases were reported by 7 states: Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin. Tickborne transmission of Babesia parasites is well established in these states.

FIGURE 1. Number of reported cases of babesiosis, by county of residence† — 22 states,§ 2012

† N = 904; county of residence was unknown for 7 of the 911 patients. Cases are mapped to the patients’ county of residence, not necessarily the place where patients became infected.

§ For 2012, 14 of the 22 states that conducted surveillance for babesiosis reported at least 1 case: California, Connecticut, Indiana, Maine, Maryland, Massachusetts, Minnesota, Nebraska, New Hampshire, New Jersey, New York, Rhode Island, Vermont, and Wisconsin. Eight (8) states reported 0 cases: Alabama, Delaware, Michigan, North Dakota, Oregon, Tennessee, Washington, and Wyoming. In 2012, babesiosis was not a reportable disease in the gray states, and health departments in those states did not notify CDC of cases.

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Although cases of babesiosis can occur during any month, the majority of people reported getting sick during the spring or summer months. Among the 638 patients for whom data were available, 459 (72%) had symptom onset dates during June–August (Figure 2).

FIGURE 2. Number of reported cases of babesiosis,† by month of symptom onset — 2012

† N = 638 with available information.

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Patient Characteristics

For 2012, the median age of the patients was 62 years, with a range from less than 1 year to 98 years (Figure 3); 63% were male, 34% were female, and the sex was unknown for 3%.

For the 633 patients with information available, 285 (45%) were hospitalized. The median length of hospital stay was 5 days (range: 1 – 32 days). Signs and symptoms were not reported for every patient. When information was available, fever was the most frequently reported sign or symptom (85%; n=557/658 patients), followed by anemia (68%; n=240/351) and thrombocytopenia (68%; n=227/333).

FIGURE 3. Number of reported cases of babesiosis, by age group† — 2012

FIGURE 3. Number of reported cases of babesiosis, by age group† — 2012

† N = 904; age was unknown for 7 of the 911 patients.

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Routes of Transmission

Of the 341 patients for whom data were available, only 147 (43%) recalled having a tick bite in the 8 weeks before symptom onset. Because the ticks that spread Babesia parasites are very small, many infected people don’t remember being bitten.

Babesiosis is usually spread by ticks, but people can also get infected via blood transfusion or congenitally (from mother to baby during pregnancy). For 2012, 7 cases of babesiosis in blood recipients were classified by the reporting state as transfusion associated; 1 reported case was attributed to congenital transmission.

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Surveillance and Reporting

CDC collects and disseminates U.S. babesiosis surveillance data. Surveillance is the ongoing collection and analysis of data and the timely dissemination of information so that action can be taken. State and territorial health departments notify CDC of cases of nationally notifiable conditions. Health care providers, laboratories, and the general public should contact their state health department for information about babesiosis reporting. For additional information visit babesiosis surveillance and case reporting.

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