Rule of 7s for Lyme Meningitis
Use in pediatric patients (aged 2–18 years) in a Lyme endemic area with CSF pleocytosis, defined as CSF WBC ≥10 cells/mm³ (corrected for CSF RBC if >500 using a ratio of 1 WBC for every 500 RBC).
In Lyme endemic areas when deciding to start antibiotics in pediatric patients who:
- Are 2–18 years old, AND
- Have undergone a lumbar puncture and CSF demonstrates pleocytosis (CSF WBC ≥10 cells/mm³, corrected for CSF RBC if >500 using a ratio of 1 WBC for every 500 RBC).
- If CSF RBC >500, CSF WBC must be corrected using a ratio of 1 WBC for every 500 RBC in the CSF cell count.
- Should not be used in settings where patients do not have access to close follow-up with a medical provider.
- Validated by a retrospective cohort study of over 400 children in Lyme endemic areas.
- Can help guide clinicians assessing the need to initiate antibiotic therapy for Lyme meningitis (LM), versus observation and close follow-up.
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- This tool should be used to assist a clinician in decision-making and not replace clinical evaluation of a patient.
- Patients with scores 1–3 are NOT low risk for Lyme meningitis, and antibiotic therapy for LM should be considered.
- Patients with scores 0 are at low risk for LM. Symptoms may be due to aseptic meningitis or other etiology. Use clinical judgment and consider availability of follow-up with both the patient and primary care provider before electing to treat patient symptoms with antibiotics.
If patient is low risk for LM, consider discharge and discuss with patient and primary care provider to ensure adequate follow-up. If patient is not low risk for LM, consider antibiotic therapy that will cover Borrelia burgdorferi, taking into account the patient’s age.
The Rule of 7s is meant to aid in the decision to start antibiotics for suspected Lyme versus aseptic meningitis. It should not replace clinical judgement and clinician assessment of patients.
Addition of the selected points:
Number of days of headache
CSF mononuclear cells
7th (or other) cranial nerve palsy
Facts & Figures
Rule of 7s
Low risk for Lyme meningitis
Not low risk for Lyme meningitis
The Rule of 7s was first proposed by Avery et al as a mathematical model examining risk factors for Lyme meningitis. Garro et al prospectively validated the rule in a study of 50 children aged 2–18 years in a Lyme endemic region. Fourteen children had LM, six had possible LM and 30 were ultimately diagnosed with aseptic meningitis. Categories of low (<10%), indeterminate (10-50%), and high (>50%) probabilities of LM were derived based on percent of CSF mononuclear cells, duration of headache and presence of cranial nerve neuropathy.
Positive predictive value with a cutoff of >50% probability of LM was 100% (95% CI 66-100%). Negative predictive value was 100% (95% CI 82-100%) with a cutoff of <10% probability of LM. The authors noted that when the patient had <7 days of headache, <70% mononuclear cells and no cranial neuropathy, the probability of LM was always less than 10%, therefore making them low risk for LM.
This study was validated in a large retrospective cohort study by Cohn and Nigrovic et al via electronic medical record data in three pediatric emergency departments in Lyme endemic areas. A sample of 423 children, aged 90 days to 19 years, included 117 who were diagnosed with Lyme meningitis and 306 who were diagnosed with aseptic meningitis. Specificity of the Rule of 7s for low risk was 41% (95% CI 36-47%), and sensitivity was 96% (95% CI 90%–99%).
Original/Primary ReferenceGarro AC, Rutman M, Simonsen K, Jaeger JL, Chapin K, Lockhart G. Prospective validation of a clinical prediction model for Lyme meningitis in children. Pediatrics. 2009;123(5):e829-34.
ValidationCohn KA, Thompson AD, Shah SS, et al. Validation of a clinical prediction rule to distinguish Lyme meningitis from aseptic meningitis. Pediatrics. 2012;129(1):e46-53.
From the Creator
Why did you develop the Rule of 7s? Was there a particular clinical experience or patient encounter that inspired you to create this tool for clinicians?
My colleagues and I in emergency medicine and infectious disease often were faced with the clinical scenario where a child was known to have meningitis but it was peak enterovirus and Lyme disease season. Because Lyme disease tests take a while to result, the treatment decision is difficult, and we felt a clinical decision tool would be a useful way to guide treating providers.
What pearls, pitfalls and/or tips do you have for users of the Rule of 7s? Do you know of cases when it has been applied, interpreted, or used inappropriately?
It has a good negative likelihood ratio for Lyme meningitis, so if the score indicates a low risk of Lyme meningitis there is no need to empirically treat. The converse is not true, so if a patient is not low risk for Lyme meningitis, it does not mean they are high risk. Rather it should be interpreted as an indeterminate risk.
What recommendations do you have for doctors once they have applied the Rule of 7s? Are there any adjustments or updates you would make to the score based on new data or practice changes?
It is crucial to communicate well with a patient's primary care provider as treatment may need to be adjusted based on serology results or changes in symptoms.
Based on European data, Lyme disease experts believe that oral antibiotics are likely adequate to treat Lyme meningitis (traditionally IV beta-lactamase antibiotics have been recommended). It is important to note that this has not been well studies in the U.S. nor in children, but will be the focus of a planned clinical trial based in the U.S.
Additionally, there is recent evidence that a course of oral doxycycline is safe in younger children (it has traditionally been avoided in children less than 8 years old). Doxycycline has good CSF penetrance and therefore if oral antibiotics are adequate to treat Lyme meningitis, doxycycline would be the preferred alternative to amoxicillin, which does not have good CSF penetrance.
How do you use the Rule of 7s in your own clinical practice? Can you give an example of a scenario in which you use it?
During the mid to late summer, when enterovirus and Lyme disease peak, I use the Rule of 7's when I have a child with meningitis but an unclear causative organism. If the rule indicates low risk of Lyme meningitis, then I do not start a child on antibiotics. If the rule indicates an indeterminate risk, I arrange close follow up with the child's primary care provider and have a discussion about empiric antibiotics pending Lyme serology results.
What qualifies as a Lyme endemic area?
The best source for up-to-date Lyme disease prevalence in the U.S. is the CDC data, which is publicly available here.
How has the Rule of 7s impacted clinical practice in your institution or other institutions in a Lyme endemic area?
It helps clinicians make real-time treatment decisions in situations where Lyme serology results are unknown / pending.
Any other research in the pipeline that you’re particularly excited about?
Pedi Lyme Net is a network of pediatric hospitals in Lyme endemic regions of the U.S. that is collecting biosamples from children with Lyme disease and Lyme disease mimics to develop novel diagnostic techniques. The goal is to identify tests that can be used with a high degree of accuracy at the point-of-care.
Additionally, we are planning a non-inferiority trial of oral doxycycline versus IV ceftriaxone for the treatment of Lyme meningitis in children in the U.S.
About the Creator
Aris Garro, MD, MPH, is an associate professor of pediatrics and emergency medicine at the Warren Alpert Medical School of Brown University in Rhode Island. He works clinically at Hasbro Children’s Hospital Emergency Department, and in 2013, he won the Outstanding Physician Award from the University Emergency Medicine Foundation. Dr. Garro’s research interests include Lyme disease, meningitis, and asthma in pediatric patients.
To view Dr. Aris Garro's publications, visit PubMed
- Matthew Lecuyer, MD