Lyme disease underreported, incidence still on the rise

  • Infectious Disease News, January 2014

Lyme disease continues to be the most commonly reported vector-borne illness in the United States and was the seventh most common nationally notifiable disease in 2012. However, there are likely many more cases that go unreported, according to the CDC.

Last year, more than 30,000 probable cases of Lyme disease were reported. In 2010, children aged 19 and younger accounted for almost 30% of the cases.

Stan L. Block, MD, FAAP, who is a professor of clinical pediatrics at the University of Kentucky College of Medicine and at the University of Louisville Medical School, as well as a private practitioner, told Infectious Disease News that it is easy to discern that the deer tick carriers of Lyme are spreading further south and west in the United States.

 

Eugene Shapiro, MD, of the Yale School of Public Health, said that he does not think the true number of Lyme disease cases is as high as the preliminary estimate from the CDC.

Source: Shapiro E

This epidemiologic change and better physician reporting probably account in part for the increased number of cases,” he said. “I have personally seen eight Lyme cases in the past 5 years, compared to maybe two cases in the prior 25 years.”

Infectious Disease News spoke with several experts about Lyme disease cases, diagnosis, treatment and prevention.

Reported cases

Three complementary studies are currently being conducted by the CDC in an attempt to better quantify how many people are actually diagnosed with Lyme disease each year. These results were presented at the 2013 International Conference on Lyme Borreliosis and other Tick-borne Diseases in August 2013. The studies include one based on medical claims information from an insurance database; data obtained from a survey of clinical laboratories; and survey data to determine the number of people reporting that they were diagnosed with Lyme disease within the past year.

“Each of these approaches has its own strengths and limitations, which is why it’s important to use multiple methods and see if they yield similar results,” Paul Mead, MD, MPH, chief of epidemiology and surveillance activity in the bacterial diseases branch of the division of vector-borne diseases at the CDC, told Infectious Disease News. “This process is underway and we hope to have it done sometime in the next year. Preliminary results suggest that the disease is underreported, which is consistent with previously published studies.”

Validity of higher estimates questioned

According to the CDC, the new estimates indicate that the number of Lyme disease cases in the United States each year is closer to 300,000. “The first thing to stress is that this is a work in progress and that these preliminary estimates are subject to change,” Mead said. “Second, it’s important to understand that these estimates do not suggest anything new with regard to the geographic distribution or clinical features of Lyme disease.”

However, Eugene Shapiro, MD, professor of pediatrics and epidemiology at the Yale School of Public Health, said that although he believes there is underreporting, he does not think that the true number of cases is as high as the preliminary estimate.

“My own belief is that there is a lot of over-reporting because there are a lot of diagnoses based on laboratory tests that are based on non-specific symptoms that are probably not Lyme disease,” he said. “There are a ton of false-positive test results.”

According to results published in 2008 in MMWR, during a 15-year surveillance conducted by the CDC, the incidence of Lyme disease more than doubled in the United States, from 9,908 cases in 1992 to 19,931 cases in 2006.

Geographic locations and seasonal onset

MMWR also reported that 93% of the cases were reported from 10 states: Connecticut, Delaware, Maryland, Massachusetts, Minnesota, New Jersey, New York, Pennsylvania, Rhode Island and Wisconsin.

These results do not correspond with previous literature, according to Block: “Interestingly, Lyme disease is rarely reported south of Virginia because ticks in southeastern states and southwestern states feed mostly on reptiles rather than small mammals and deer.”

In addition, more than 65% of patients with erythema migrans had onset of illness in June and July.

“Just like the other rarer arthropod-borne diseases, Rocky Mountain spotted fever and ehrlichiosis, the primary season for Lyme disease is April through October, with the peak during the summer months,” Block wrote.

Diagnosis methods and stages of disease

Clinical diagnosis is recommended for Lyme disease, especially in the early stages when the typical erythema migrans rash is most likely to be present, according to Mead.

“The early stages of Lyme disease is diagnosed strictly on the clinical observation of a solitary erythema migrans lesions of at least 5 cm, with or without a history of deer tick attachment,” Block wrote in a report. “Borrelia antibody titers are not detectable in most people within the first 4 weeks following the appearance of erythema migrans.”

Erythema migrans is localized in 80% to 90% of cases and typically appears at the site of the bite within 7 to 14 days (range 3-32 days). The rash also typically spreads in the 5 to 7 days after detachment of the tick, according to the AAP Red Book.

“Contrary to popular opinion, only about 10% to 15% of erythema migrans rashes are true bull’s-eyes,” Shapiro told Infectious Disease News. “About two-thirds are uniformly red or they have enhanced central erythema, but they don’t necessarily have that clear area around it; some do, but it’s relatively uncommon.”

According to a presentation at the 25th Annual Infectious Diseases in Children Symposium by Margaret C. Fisher, MD, who is the medical director at The Unterberg Children’s Hospital at Monmouth Medical Center in Long Branch, N.J., patient history is important when diagnosing Lyme disease and should be considered.

“The patient must have resided or traveled to an area where Ixodes ticks are present, and they must have spent time in an activity that would allow them to be bitten by a tick,” she said. “The clinical findings should suggest and be consistent with Lyme disease.”

Most often, people get Lyme disease from a tick they were not aware of, Shapiro said.

“Three-quarters of people who recognize that a tick bit them pull it out within 48 hours. Even if it’s an infected tick, generally it must have been feeding for at least 36 to 48 hours to transmit the infection,” Shapiro said. “It’s the tick you don’t see that is more likely to transmit the infection than those that you do see. A history of a tick bite is more of a marker that somebody is at risk of exposure.”

During the early disseminated disease stage, clinicians should be aware of the possibility of multiple erythema migrans.

Margaret C. Fisher

Margaret C. Fisher

“It may also cause other manifestations, including neurologic involvement, cranial nerve palsy, meningitis and carditis, which are relatively rare,” Shapiro said. “Those are the main manifestations of early disseminated Lyme disease.”

Late Lyme disease is often characterized by arthritis, generally pauciarticular, and most often involving the knees.

“It is interesting that in reported cases, arthritis seems to be a bit more common in children than adults, but there are a number of caveats when evaluating clinical features from surveillance data,” Mead said. “Early stages of disease may be less likely to be reported than later stages, so that can skew the results.”

Shapiro said some experts argue over the existence of Lyme encephalitis, which is a late manifestation of central nervous system infection.

“This is extraordinarily rare. You almost never see it anymore because people recognize the earlier stages of the disease,” he said.

According to Mead, after clinical diagnosis, the most commonly recommended method for diagnosis is using serology, which does not detect the organism itself, but antibodies made to the organism.

“It’s a useful tool, but as with other serologic tests, there is a window period between the time of infection and time when the patient has developed sufficient antibodies to have a positive test,” he said. “When a patient presents with erythema migrans the test is frequently still negative. This is why it’s recommended that patients who have symptoms of early Lyme disease be treated regardless of serologic test results. Conversely, patients with long-standing signs have had time to develop an antibody response, so a negative test should not be ignored.”

Samir S. Shah, MD, MSCE, a pediatric infectious disease physician, director of the division of hospital medicine at Cincinnati Children’s Hospital, said defining the incidence of Lyme disease is especially challenging.

“Antibody titers may not be elevated with early localized disease; as a result, antibody testing is not routinely recommended in these circumstances and the physician must recognize the pattern of the rash,” he told Infectious Disease News. “This strategy, while reasonable, may lead to either over or underestimates of disease prevalence. Additionally, false-positive test results occur, especially in areas of low Lyme disease prevalence, where positive test results are more likely to represent false-positive results, and in patients with non-specific symptoms. Unfortunately, non-specific symptoms such as fatigue are often attributed to Lyme disease; physicians should pursue alternate diagnoses when symptoms are non-specific or subjective.”

Treatment options

According to the Infectious Diseases Society of America, most infections can be treated with antimicrobials.

“Typically, you treat early Lyme disease with doxycycline. Pregnant women or children under 8 years of age are treated with amoxicillin. Cefuroxime is another option,” Shapiro said. “Those are all given orally for 10 to 21 days, 10 days for doxycycline and 14 days for amoxicillin or cefuroximefor early localized disease, and 14 to 21 days for early disseminated disease.”

Lyme meningitis can be treated with intravenously administered ceftriaxone, he said.

“Remember that first-generation cephalosporins and macrolides are generally considered ineffective, and the preferred choice of cefuroxime suspension is actually unpalatable,” Block said. “Practically speaking, the palatable cefdinir or cefprozil antibiotics may be better oral choice for failures or non-highly penicillin allergic children.”

Prevention of Lyme disease relies on avoidance of tick bites or prompt removal of the tick before transmission of the spirochete occurs, according to Fisher.

“Ticks are most common in high grass or weeds. In general, if you can see your shoes, you are not likely to be bitten. This was shown in a study of golfers that correlated the likelihood of Lyme disease with time spent in the rough. Tick checks are important so that the tick can be removed promptly,” she said.

According to a 2012 presentation by Gordon E. Schutze, MD, who is a professor of pediatrics at Baylor College of Medicine, reducing exposure to tick bites is one of the best ways to prevent them.

“Barriers and environmental controls are important,” he said. “They always tell you to wear long pants, long shirt, and tuck your pants into your socks or boots.”

Shah added that may be especially challenging for parents to get their children to do this.

“Therefore, physicians should also emphasize ‘tick checks’ with prompt removal of attached ticks,” he said. “These checks should be performed after any activity that could result in tick exposure.”

Skin repellents also are recommended when they contain 20% to 30% or more of DEET, and Schutze said these appear to be safe for use in children.

“It’s important for you to remember that there is no data that says non-DEET-containing repellents are safer than DEET-containing repellents,” Schutze said. “That’s why the AAP and CDC continue to push DEET as the No. 1 primary repellent. DEET is the gold standard.”

A Lyme disease vaccine (Lymerix, GlaxoSmithKline) was available in the United States from 1998 to 2002, but was removed from the market. Currently, there are no vaccines available for tick-borne diseases in the United States.

Other common vector-borne diseases

Other most common tick-borne diseases in the United States include Rocky Mountain spotted fever, anaplasmosis, ehrlichiosis and babesiosis.

According to Mead, the tick that transmits Lyme disease also can transmit several other pathogens, including anaplasmosis (about 2,400 cases reported in 2012) and babesiosis (about 940 cases reported in 2012).

“Babesiosis is a parasitic disease that produces a malaria-like illness,” he said.

About 1,000 cases of ehrlichiosis are also reported each year, but is transmitted by Amblyomma americanum. According to the CDC website, about 2,500 cases of Rocky Mountain spotted fever are reported annually. This disease is transmitted by the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (D. andersoni) and brown dog tick (Rhipicephalus sanguineus), and is more common in the southeastern and southern United States.

“That’s a very important disease because it can be deadly,” Mead said of Rocky Mountain spotted fever.

According to Shapiro, Rocky Mountain spotted fever and ehrlichiosis generally, but not always, result in more severe illness than anaplasmosis or babesiosis. Rocky Mountain spotted fever also can cause meningitis and has a significant mortality rate if it is not treated. – by Amber Cox

References:

AAP. Section 3: Summaries of Infectious Diseases: Lyme Disease. In: Pickering LK, ed. Red Book: 2012 Report of the Committee on Infectious Diseases, 29th edition. Elk Grove Village, IL: American Academy of Pediatrics; 2012.
Block SL. Pediatr Ann. 2013;42:57-60.
CDC. MMWR. 2008;57:1-9.
CDC. Rocky Mountain spotted fever. Available at: www.cdc.gov/rmsf/. Accessed Nov. 11, 2013.
Fisher M. Lyme disease: fact and fiction. Presented at: 2012 IDC NY; Nov. 17-18, 2012; New York.
IDSA. Lyme Disease. Available at: www.idsociety.org/Lyme/. Accessed Nov. 11, 2013.
Mead P. Estimating the public health burden of Lyme disease in the United States: preliminary results from a work in progress. Presented at: 2013 International Conference on Lyme Borreliosis and Other Tick-Borne Diseases; Aug. 18-21, 2013; Boston.
Schutze GE. Once bitten, twice shy: preventing mosquito and tick bites. Presented at: 2012 IDC NY; Nov. 17-18, 2012; New York.

For more information:

Stan L. Block, MD, FAAP, can be reached at: 
slblockmd@hotmail.com.
Paul Mead, MD, MPH, can be reached at 3650 Rampart Road, Ft. Collins, CO 80521.
Margaret C. Fisher, MD, Gordon E. Schutze, MD, Samir S. Shah, MD, and Eugene Shapiro, MD, did not provide contact information.

Disclosure: The researchers report no relevant financial disclosures.

 

The true incidence of Lyme disease has been debated in recent years. Why?

POINT

The CDC reports on the number of diagnosed cases, including insurance claims and patient self-reports, which may be inaccurate.

We have known for many years that Lyme disease is significantly underreported. In fact it has been suggested for quite some time that the actual number of cases may be 10-fold higher than the number captured by surveillance methods. It is certainly a challenge to expect busy physicians to report every case they see of a common disease, as well as mobilizing public health personnel to verify these cases. The 300,000 figure, therefore, is actually not surprising.

It should be mentioned that the new CDC study does not report cases of Lyme disease — it is reporting diagnoses of Lyme disease. This is based on a number of data sources, including insurance claims and patient self-reports. The number may therefore be inaccurate, and cases cannot be categorized, according to CDC surveillance definitions of the infection. Nonetheless, it certainly communicates that the number of diagnoses greatly exceeds the number of cases captured by traditional disease surveillance.

There are two important points that practicing clinicians should keep in mind. First, these excess cases are occurring in the same states where the disease is known to be heavily transmitted. More than 95% of all Lyme disease cases are transmitted in just 13 northeastern and upper Midwestern states; the new 300,000 figure does not challenge the geography of Lyme disease transmission. Second, these new CDC data are not published — so we should avoid overinterpretation until they have undergone peer review.Paul M. Lantos, MD, is with the department of pediatrics at Duke University School of Medicine. Disclosure: Lantos reports no relevant financial disclosures.

 

COUNTER

An essential requirement of the reporting process is a diagnostic test but antibodies are not detectable in the blood until about 4 to 5 weeks after infection.

A recent presentation by the CDC indicates that the number of reported cases of Lyme disease may be under-reported by as much as 300,000 per year. However, keep in mind that although these additional cases are not reported to the CDC — for various reasons-- all of them represent patients who have been treated since the data was derived from health insurance records from patients who have been treated for Lyme disease, but whose cases have not been reported to the CDC.

It is incorrect to assume that under-reporting means that large numbers of people with Lyme disease are invariably untreated. This complicates the interpretation of data with regard to reported cases. But, it does not seem to be any different from the situation with other reported infectious disease where there is under-reporting of about the same magnitude.

Physicians are very busy people — you can’t make them report these cases. Sometimes when they encounter a patient with Lyme disease, it is too early to provide information on the results of a diagnostic test — which is an essential requirement of the reporting process — simply because antibodies are not detectable in the blood until about 4 to 5 weeks after infection. While all of these issues make reporting more difficult, it is most likely that there are many people being treated correctly for Lyme disease — based on a clinical judgment, not laboratory tests — than are reported, especially if such cases occur in endemic areas where physicians are aware of Lyme disease and its symptoms.

Philip J. Baker, PhD, is the executive director of the American Lyme Disease Foundation. Disclosure: Baker reports no relevant financial disclosures.