Infectious Disease Pearls

  1. Can herpes zoster recur in immunocompetent persons?
    -YES, zoster can recur in immunocompetent persons, even soon after the initial episode
  2. What medications are most commonly implicated as the cause of Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis?
    The most commonly implicated medications are antibiotics, including penicillins and sulfonamides, with the latter implicated more often than cephalosporins
  3. When evaluating a patient in the ED with meningitis, the clinician must make treatment decisions based, at least in part, on the evaluation of the CSF. When the rest of the clinical picture strongly suggests viral meningitis, recognize that the finding of a preponderance of ? is not incongruous with the diagnosis.
    -Polymorphonuclear cells (PMNs)

    Typically, aseptic meningitis is associated with mononuclear cell preponderance. However, this may often be preceded by a transient predominance of PMN’s in the CSF for up to 48 hours, and perhaps longer. One report of a pediatric population found that a majority of children with aseptic meningitis (57%) had a predominance of PMN’s during enteroviral season and that this persisted in many patients beyond 48 hours (2).

    References:(1) Graham TP. Myth: Cerebrospinal fluid analysis can differentiate bacterial meningitis from aseptic meningitis CJEM 2003;5(5):348-9.(2) Negrini B, et. al. Cerebrospinal Fluid Findings in Aseptic Versus Bacterial Meningitis PEDIATRICS 2000;105: 316-9.(3) Zunt JR Cerebrospinal fluid testing for the diagnosis of central nervous system infection Neurol Clin 1999;17: 675-89.
  4. The prevalence of HIV infection among incarcerated persons in the US is four times greater than the prevalence among persons in community settings. What is the prevalence of each?
    The prevalence of HIV infection among incarcerated persons in the US is 1.5%; among persons in community settings it is 0.4% (MMWR, June 25, 2010).
  5. Most important risk factor for death from West Nile Virus:
    Advanced age is the most important risk factor for death from WNV.
  6. Typical CSF analysis of patients with West Nile Virus and neurologic symptoms:
    CSF analysis of patients with neurologic disease typically demonstrates an aseptic meningitis-like pattern: elevated protein, near-normal glucose, and pleocytosis with a predominance of lymphocytes (rather than neutrophils).

    Ninety percent of patients with meningoencephalitis will have IgM antibody in their CSF within 8 days of symptom onset.
  7. How do you diagnose West Nile Virus?
    Diagnosis of WNV is made by serology, by detection of IgM antibody in either serum or CSF.
  8. True or false: Most people with West Nile Virus remain asymptomatic.
    True: About 20% to 30% of infected patients experience an acute, febrile, influenza-like illness.
  9. With the advent of vaccination for Haemophilus influenzae type B, acute epiglottitis presentations to EDs are now more commonly reported among adults than among children. Do adults require emergent airway interventions as frequently as children?
    In a literature review, just 15–33% of acute adult epiglottitis required emergent airway interventions (JEM, In Press, Online 7/23/10).
  10. Why are the atypical pneumonia pathogens referred to as atypical?
    They are "atypical" in the sense that they are not detectable on Gram stain or cultivatable on standard bacteriologic media (Clin Inf Dis; 44:S27).
  11. What type of virus is West Nile Virus?
    Mosquito born RNA virus from the family Flavivirus
  12. What percentage of individuals develop an acute, febrile, influenza-like illness?
    Only 20-30%
  13. What percentage of patients with WNV develop neurologic disease?
  14. Postinfectious glomerulonephritis is induced by infection with specific strains of group A Beta-hemolytic streptococci. Does it only occur following pharyngitis? How long after infection does the hematuria typically occur?
    Postinfectious glomerulonephritis is most commonly preceded by symptoms of either pharyngitis or impetigo, with a latent period from infection to hematuria of 10 and 21 days, respectively (Mayo Clin Proc, Vol. 84, pg. 72).
  15. On urine dipstick, urine nitrites have a low sensitivity but high specificity for the diagnosis of UTI. Name an important bacterial species that does not convert nitrates to nitrites, thereby giving a false negative test.
    Enterococcus species do not convert nitrates to nitrites (JEM, 7/10, pg. 6).
  16. Most episodes of febrile neutropenia occur in patients receiving chemotherapy. When does the neutrophil nadir typically occur after the last dose?
    For most outpatient chemotherapy, the neutrophil nadir typically occurs 5 to 10 days after the last dose (Mayo Clin Proc, Vol. 81, pg. 843).
  17. What is the leading cause of reported foodborne disease outbreaks?
    Norovirus is the leading cause of reported outbreaks and outbreak-related illnesses (MMWR, August 13, 2010).
  18. The 2010 guidelines from the CDC for the upcoming influenza season recommend routine influenza vaccination for all persons over what age?
    Routine influenza vaccination is recommended for all persons aged 6 months or older. This represents an expansion of the previous recommendations for annual vaccination of all adults aged 19-49 years (MMWR, 8/6/10).
  19. The CDC has recommended a 5-dose rabies vaccination regimen for postexposure prophylaxis to prevent human rabies. How has this recommendation recently changed?
    As of 2010, new recommendations reduce the number of vaccine doses to four (MMWR, March 19, 2010).
  20. The number of rabies vaccines recommended by the ACIP (Advisory Committee on Immunization Practices) has been reduced from 5 to 4 doses for unvaccinated patients. Why?
    This was based on evidence from multiple source, including pathogenesis data, animal trials, clinical studies, and epidemiological surveillance.

    The first dose of the 4-dose regimen should be administered as soon as possible after exposure (day 0). Additional doses are then given on day 3, 7, and 14. The first dose of rabies vaccine should be administered with HRIG, infiltrating as much as possible into the wound, with the remainder given IM at a distant site from the vaccine.

    This recommendation is not applicable to immunocompromised patients, who should continue to receive the full five doses.

    Sullivan, DM. Update on Emerging Infections: News from the Centers for Disease Control and Prevention. Infectious disease/CDC Update. Ann Em Med July 2010;56(1):64-6.
  21. An acute a diarrheal illness has been observed to result in excessive anticoagulation from warfarin. How does a diarrheal illness potentiate warfarin activity?
    Oral intake of nutrients declines, Vitamin K absorption is less, the in vitro source of vitamin K from bacterial flora decreases, and dehydration increases the relative concentration of warfarin in the blood (JAMA, Vol. 279, pg. 657).
  22. When treating a patient with herpes zoster (shingles) what is the effect of corticosteroids on the development of postherpetic neuralgia?
    Corticosteroids DO NOT have any effect on PHN (Mayo Clin Proc, Vol. 84, pg. 274).
  23. Emergency Physicians not uncommonly evaluate patients presenting with diarrhea from C difficile infection. Should you recommend a follow up C difficile stool toxin assay after treatment has been completed to ensure that the patient is cured?
    Because stool toxin assays remain positive during and after successful treatment, follow-up stool toxin assays for test of cure should be avoided

    (Mayo Clin Proc, 2/10, pg. 172).
  24. What is the most common infectious agent associated with Stevens-Johnson Syndrome?
    Mycoplasma pneumoniae is a well-known cause of SJS.

    It usually affects children and young adults and has been reported as the most common infectious agent associated with SJS (Mayo Clin Proc, 2/10, pg. 131).
  25. Can meningitis develop after lumbar puncture?
    Meningitis develops after LP in approximately 1 in 50,000 cases, with about 80 cases reported annually in the US.

    The majority of cases occur after spinal anesthesia or myelography (NEJM, 1/14/10, pg. 146).
  26. A patient presents to the ED concerned about the possible development of Lyme disease after having found a deer tick on her leg. She is sure that the tick was attached for no longer than 6 hours. How concerned should she be?
    • During the first 15 hours of tick attachment, the spirochetes are restricted to the tick gut; after 48 hours they move to the salivary glands, supporting data showing a low infection risk within 36 hours of tick attachment
    • (Mayo Clin Proc, 4/10,e13)
  27. True or False: Isolated limb pain is an early presenting feature in up to 50% of children with meningococcal disease?
    True. Isolated severe limb pain in the absence of any other physical signs in the limb is a well-established phenomenon in meningococcal disease (Emerg Med J, Vol. 26:229).
  28. The lesions of herpes zoster through stages, beginning as red macules and papules that, in the course of 7 - 10 days, evolve into vesicles and form pustules and crusts. How long does complete healing take?
    • Complete healing may take more than 4 weeks
    • (Mayo Clin Proc, Vol. 84, pg. 274).
  29. Occasionally, herpes zoster (shingles) can cause motor weakness in noncranial nerve distributions, called zoster paresis. How does it present? What is the progrnosis?
    The mechanism of zoster paresis has not been determined. Weakness develops abruptly within 2-3 weeks after the rash and can involve upper or lower extremities. The prognosis of zoster paresis is good

    (MMWR, Vol. 57 /No. RR-5)
  30. CSF diagnoses of meningitis:
    Bacterial Meningitis >> Milky CSF with increased protein, decreased glucose, high WBC's, few RBC's, mildly increased opening pressure, normal % gamma globulin.

    Viral Meningitis >> Cloudy CSF with increased protein, normal glucose, increased WBC's (lymphocyte predominant), no RBC's, normal opening pressure, normal % gamma globulin.

    Herpes Simplex Encephalitis >> Cloudy CSF with increased protein, normal glucose, increased WBC's (lymphocyte predominant), few RBC's, increased opening pressure, normal % gamma globulin.

    Subarachnoid Hemorrhage >> Yellow CSF with increased protein, normal glucose, few WBC's, inumerable RBC's, mildly increased opening pressure, normal % gamma globulin.
  31. Symptoms of acute HIV are non-specific. 2 recent studies found that among ED patients presenting with non-specific viral illnesses or tested specifically for EBV, 1–2% were found to have acute HIV. What testing is diagnostic of acute HIV syndrome?
    A high HIV RNA viral load in the absence of antibodies is diagnostic of acute HIV. The HIV RNA viral load will usually be positive within 11 days of exposure

    (JEM, In Press, Online 10/1510).
  32. Why does Staphylococcal scalded skin syndrome usually occur in children?
    Staphylococcal scalded skin syndrome usually occurs in children, as adults have specific antistaphylococcal antibodies to excrete the staphylococcal toxin through adequate renal clearance

    (Mayo Clin Proc, Vol. 84, pg. 838).
  33. Why do bacterial infections of the CNS result in a low CSF glucose concentration (CSF-to-serum ratio <0.4)?
    • A low CSF glucose concentration is primarily a result of impaired functioning of the glucose transporter system across the blood-brain barrier
    • (Mayo Clin Proc, Vol. 82, pg. 874).
  34. Since bacterial conjunctivitis is usually a self-limiting disease, why are topical antibiotics commonly prescribed?
    • Treatment:
    • -shortens the course
    • -reduces person-to-person contact
    • -lowers the risk of sight-threatening complications such as ulceration

    (EMCNA, Vol. 26, pg. 40).
  35. What bacterial enteric infection causes hemolytic-uremic syndrome? What is the mechanism?
    This syndrome is caused by Shiga toxin-producing E. coli. Shiga toxin is absorbed, causing injury to endothelial cells of the glomerular capillaries with intravascular coagulation

  36. What is the treatment for Cutaneous larva migrans?
    CLM is generally self-limited; most patients need only supportive measures. However, the intense pruritus and risk of secondary infection often mandate treatment. Thiabendazole is the first-line agent.

    (JEM In Press, Online 2/20/10).
  37. A nursing home patient is sent to the ED for management of a positive toxin assay for C. difficile. This was obtained as follow up to recent antibiotic treatment of C. diff infection. The patient is now asymptomatic. What management warranted?
    A positive toxin assay for C. difficile in a patient with minimal or no symptoms should not propmpt treatment

    (NEJM, Vol. 359, pg. 1932).
  38. When in the course of the illness is shingles contagious? Is it more or less contagious that chickenpox?
    Less contagious than primary varicella, herpes zoster is only contagious after the rash appears and until the lesions crust. Risk of transmission is reduced further if lesions are covered

    (Mayo Clin Proc, Vol. 84, pg. 274).
  39. Pregnant women in the US should be tested for HIV infection as early during pregnancy as possible. In the absence of antiretroviral and other interventions, what portion of infants born to HIV-infected mothers will become infected with HIV?
    In the absence of interventions, 15-25% of infants born to HIV-infected mothers will become infected with HIV; another 12-14% born to infected mothers who breastfeed into the 2nd year of life will become infected (MMWR, 59(RR12).
  40. Which antibiotic is recommended as the first-line agent for treating patients with severe infection with C. difficile?
    Vancomycin can now be recommended as the first-line agent in patients with severe infection because of more prompt symptom resolution and a significantly lower risk of treatment failure

    (NEJM, Vol. 359, pg. 1932).
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Infectious Disease Pearls
Infectious Disease Pearls