When and How to Test for Lyme Disease, a Growing Threat
Both Canada's Public Health Agency and the CDC recommend a 2-tiered testing process for a patient with suspected Lyme disease.
The Centers for Disease Control and Prevention (CDC) estimates that approximately 300,000 people in the United States receive a Lyme disease (LD) diagnosis each year.1 According to the CDC, LD is the nation's most commonly reported vector-borne illness.2 The highest incidence of LD is in Northeastern states plus Minnesota, Wisconsin, and Virginia.1,3 Lyme disease also occurs in Canada and many European countries.4,5 The territorial range of the black-legged ticks that carry the bacterium responsible for LD, Borrelia burgodorferi, is spreading throughout North America and Europe, and some experts attribute the ticks' rapid expansion to climate change.6 Anticipating increases in the incidence of LD, researchers have been examining best practices for diagnosis and management.7
Lisa Waddell, PhD, and colleagues at the Public Health Agency of Canada (PHAC) recently performed a systematic review of protocols and laboratory tests used to diagnose LD in North America, including 2-tier serological tests, immunoblot assays, and clinical diagnosis. Infectious Disease Advisor interviewed Dr Waddell about LD testing and her findings. Alison Hinckley, PhD, an epidemiologist with the CDC, also spoke with Infectious Disease Advisor regarding the agency's recommendations for evaluating US patients suspected of having LD. The 2 expert's responses reveal great concordance among the CDC, PHAC, and European organizations in the approach to diagnosing LD.8
Infectious Disease Advisor: Compared with 2016, has there been any change in the incidence or patterns of LD in the United States in 2017, which some experts predicted because of the relatively mild winter in 2016?
Alison Hinckley, PhD: Predicting the incidence of LD or other tickborne infections and how an upcoming season will compare to previous years is complicated. The lifecycle of ticks known to spread disease to humans may last 2 to 3 years, and many factors affect their numbers, including temperature, rainfall, humidity, and the number of available hosts for the ticks to feed on, such as mice and deer.
In any given year, the number of ticks (and cases of LD) in an area differs from region to region, state to state, and even county to county. We are currently finalizing LD surveillance data for 2016. Final annual case counts are published once the year has ended and all states and territories have verified their data. A table with the final 2016 data will be published in the near future at www.cdc.gov/lyme/stats/index.html.
Infectious Disease Advisor: What symptoms besides erythema migrans (EM), the bullseye rash considered a hallmark of LD, are suggestive of LD?
Dr Hinckley: General signs and symptoms that might prompt testing for LD in an area where it is common include fever, chills, headache, fatigue, muscle and joint aches, and swollen lymph nodes.
More serious symptoms include arthritis with severe joint pain and swelling, particularly of the knees and other large joints; facial palsy; heart palpitations; and an irregular heartbeat. For a complete list, see www.cdc.gov/lyme/signs_symptoms/index.html.
It's important to ask patients whether they've spent time outdoors in an area in which ticks and LD are common or if they recall getting a tick bite. If you are in a region in which LD is rare but suspect the patient has LD, consider taking a thorough travel history.
Infectious Disease Advisor: Why do you recommend against testing for LD in patients with nonspecific symptoms?
Lisa Waddell, PhD: Lyme disease symptoms mimic those of other illnesses, so diagnosing LD correctly usually involves 3 things:
- The physician's assessment of the patient
- Evidence or history that the patient could have encountered black-legged ticks, which carry LD
- The results of laboratory testing
Blood test results may be negative in patients with early LD or in patients who have had antibiotic treatment. This should be taken into consideration during diagnosis. However, the accuracy of blood tests becomes more reliable as the infection progresses. All laboratory tests should be used as supportive evidence for physicians' examinations, which is why LD should be diagnosed clinically first and foremost.
As for laboratory testing, the concern is that if you test for LD in patients who do not meet the above criteria you run the risk of a false positive. It's just as important to diagnose LD correctly when a patient has it as it is to avoid misdiagnosis and treatment when the true cause of the illness is something else.