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    Rule of 7s for Lyme Meningitis

    Distinguishes Lyme meningitis from aseptic 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).

    When to Use
    Why Use

    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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    Next Steps
    Creator Insights
    Dr. Aris Garro

    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

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    MDCalc loves calculator creators – researchers who, through intelligent and often complex methods, discover tools that describe scientific facts that can then be applied in practice. These are real scientific discoveries about the nature of the human body, which can be invaluable to physicians taking care of patients.
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