This time of year, the U.S. is crawling with ticks. It’s a concern because the rapacious bloodsuckers spread disease when they bite. The most common tick-borne ailment is Lyme disease, but the official case count—which helps public-health authorities formulate prevention strategies and allocate resources—doesn’t come close to the actual number. Around 30,000 cases of Lyme disease are documented each year, according to surveillance figures published annually by the Centers for Disease Control and Prevention. The real number, the agency says, is more like 300,000. “We know Lyme disease is underreported,” said Kiersten Kugeler, an epidemiologist with the CDC. “It is the most common vector-borne disease by far.” Several things may contribute to the undercount. The perception that the disease is uncommon may cut down on diagnoses. Because the counting methods used in some high-incidence states don’t adhere to official surveillance rules, the numbers are discarded. And a new rule requiring most states to produce laboratory evidence of the disease may reduce participation. “All reportable diseases are subject to underreporting, although we know this is particularly true for common diseases and those often treated in an outpatient setting,” Dr Kugeler said.
Lyme is one of more than 70 infectious diseases monitored by the CDC’s National Notifiable Diseases Surveillance System. Although the CDC publishes the figures, states collect the data based on rules set by the Council of State and Territorial Epidemiologists. Fourteen high-incidence states account for 95% of confirmed cases reported to the CDC. Since 2017, low-incidence states can only report cases with laboratory evidence of infection, while high-incidence states are still able to report cases with the classic rash associated with the disease absent laboratory evidence. Still, to streamline the process, some high-incidence states have taken a different approach. In New York, counties with the largest Lyme burden investigate only 20% of positive laboratory reports and then extrapolate to estimate the full number of cases. But the CDC won’t accept estimates. Consequently, in 2016, New York recorded 6,597 Lyme cases, but the CDC listed only 2,623 for the state. Such disparities, combined with suspected underdiagnosis and differing rules for low-incidence states, have advocates worried. “Doctors look at the CDC numbers and see low numbers for their areas and aren’t vigilant about it,” said Mary Beth Pfeiffer, author of “Lyme: The First Epidemic of Climate Change.” “The numbers should say to doctors; This is a huge problem with hundreds of thousands of cases.”
It’s difficult to say precisely what effect the latest rules will have on the surveillance numbers. The first report using them won’t be released until fall, but there is already evidence that Lyme is more abundant in some low-incidence states that the surveillance suggests. In 2016, Fair Health, a non-profit organisation that oversees the nation’s largest collection of health-care claims data, examined 23 billion records for more than 150 million privately insured individuals and documented 747,101 claims for Lyme disease. Nine of the CDC’s high-incidence states were among those submitting the largest number of claims—but so were several low-incidence states. North Carolina reported 32 Lyme cases to the CDC in 2016 but in the same year made 88,539 health-care claims for a Lyme diagnosis. California reported 90 cases to the CDC but had 46,820 claims. Texas reported 31 cases to the CDC but had 31,129 claims. All three are considered low-incidence states. Fair Health warns that its numbers don’t represent individuals with the disease but rather the number of encounters those with a Lyme diagnosis had with the health-care system.
Lyme disease can be treated successfully with antibiotics, but if undiagnosed or inadequately treated, the consequences may be severe. Lyme arthritis, causing painful swelling especially of the knee, is the most common symptom of late-stage infection. The disease can also interfere with the electrical signals that coordinate the beating of the heart and cause neurological problems such as facial paralysis and visual disturbances. Researchers from Johns Hopkins estimate that Lyme costs the U.S. health-care system between $712 million and $1.3 billion a year. Two species of ticks are known to transmit the disease: the black-legged tick, also known as the deer tick, found in the eastern half of the country, and the western black-legged tick found on the west coast. In heavily infested regions, 20% to 40% of nymphs—newly hatched ticks about the size of a poppy seed—carry the bacteria that causes Lyme, said Richard Ostfeld, a disease ecologist with the Cary Institute of Ecosystem Studies in Millbrook, N.Y. Those tiny ticks are responsible for most transmissions.
Even given a significant undercount, Dr Kugeler said the surveillance numbers have worked for the CDC by showing the geographic expansion of the disease over time and the demographics of those affected. But, she said, the system isn’t ideal for tracking a widespread illness like Lyme. “Public-health surveillance works best for rare or severe conditions,” she said. “It’s not as good at ensuring all cases are documented if it’s a common condition.”
Credit: Jo Craven McGinty for The Wall Street Journal, 22 June 2018.