Bloodstream Infection in Patients with Lyme Disease

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The summary below is from the full report titled "Brief Communication: Hematogenous Dissemination in Early Lyme Disease." It is in the 3 May 2005 issue of Annals of Internal Medicine (volume 142, pages 751-755). The authors are G.P. Wormser, D. McKenna, J. Carlin, R.B. Nadelman, L.F. Cavaliere, D. Holmgren, D.W. Byrne, and J. Nowakowski.

What is the problem and what is known about it so far?

Deer ticks sometimes carry bacteria that cause Lyme disease. These bacteria can infect humans when the ticks bite the skin. A sign of infection with Lyme disease is the development of a large red spot (known as erythema migrans) that appears at the site of the tick bite. The infection can spread to other areas of the skin (causing additional red spots) and to other organs of the body. Doctors have assumed that infection spreads from one part of the body to another through the bloodstream. Until recently, they could not prove this theory because they had difficulty growing Lyme disease bacteria from blood samples. Using newer laboratory techniques and larger samples of blood, doctors can now grow Lyme disease bacteria from blood.

Why did the researchers do this particular study?

To describe the symptoms and laboratory features of patients whose Lyme disease infection has spread to the bloodstream.

Who was studied?

213 patients with erythema migrans: 93 of these patients had bloodstream infection (positive blood cultures), and 120 did not (negative blood cultures).

How was the study done?

The investigators recorded symptoms as present or absent and then graded them according to severity. In addition, skin biopsy samples were taken from the edge of a red spot and a blood sample was drawn to try to grow the bacteria.

What did the researchers find?

Forty-four percent of patients with erythema migrans had bloodstream infection with Lyme disease bacteria. Patients with bloodstream infection were more likely to have symptoms (and more severe symptoms) than those who did not. Specifically, those with bloodstream infection more commonly had chills or fever, headache, and stiff neck and were more likely to have enlarged lymph nodes. In addition, patients with bloodstream infection often had more than one erythema migrans red spot and were more likely to have bacteria that could be grown from a skin biopsy sample. Even so, no single symptom or combination of symptoms could reliably predict which patient had bloodstream infection since some patients had similar findings even when blood cultures were negative. The risk for bloodstream infection remained high for more than 2 weeks after the first red spot appeared.

What were the limitations of the study?

The researchers had no follow-up information that would allow them to determine the long-term implications of invasion of the bloodstream with Lyme disease bacteria.

What are the implications of the study?

Bloodstream infection occurs frequently in patients with erythema migrans, increases the likelihood and severity of many symptoms, and probably explains how the disease spreads from the skin to other organs. Prolonged duration of risk for bloodstream infection may increase the chances of spread to other organs of the body.