January 28, 2013
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Definition of HGA influenced rates of coinfection with Lyme disease

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The frequency of coinfection with human granulocytic anaplasmosis and Lyme disease, as well as the severity of illness, depended on the definition used for human granulocytic anaplasmosis.

According to the study, published in Clinical Infectious Diseases, the frequency of coinfection for Lyme disease and human granulocytic anaplasmosis (HGA), both transmitted by Ixodes scapularis ticks, varied from 2% to 11.7% in three different studies.

For the current study, conducted by researchers at New York Medical College, coinfection rates varied from 2.3% to 10%. If the disease was defined based only on a positive culture for Anaplasma phagocytophilum (group A), which was the primary definition, the rate was 2.3%. When a positive culture and/or a fourfold increase in antibodies to at least 1:640 was used (group B), the rate was 5%. When a titer of 1:2,560 was included, regardless of whether there was a fourfold rise (group C), the rate increased to 7.7%. Lastly, when either a positive culture or a titer of 1:640 or more was used (group D), the rate was 10%.

The study included 311 patients with erythema migrans that were tested for HGA. The researchers compared demographic, clinical and laboratory results from patients with evidence of coinfection with 44 patients who had confirmed HGA alone.

Regardless of the definition used for coinfection, the temperature of the coinfected patients was lower than that for patients with HGA alone. The frequency of fever, sweats or rigors was lower in groups C and D compared with HGA alone. However, there was no difference in the number of symptoms between those with HGA alone and those with coinfection, regardless of the definition used. Patients with HGA alone experience more leukopenia and thrombocytopenia than patients in groups B, C or D.

Patients in group B, but none of the other groups, had more symptoms than patients with Lyme disease alone. These patients were also more likely to have fever, sweats, rigors or headache. Patients in group A were more likely to have leucopenia or thrombocytopenia.

“The results of this study indicate at least in part why there are conflicting data in the literature on whether Lyme-HGA coinfected patients have more symptoms than patients with Lyme disease alone,” the researchers wrote. “How HGA is defined in patients with erythema migrans is clearly one factor that can account for such disparate findings.”

Disclosure: The researchers report no relevant disclosures.