Immune System 1 out of 150
An 18-year-old woman is brought to the emergency department because of a 1-day history of severe headache with photophobia and diffuse myalgias. She is a college student and lives in a dormitory in a large urban area. She has not traveled recently. On arrival, she is lethargic. Her temperature is 39.3°C (102.7°F), pulse is 120/min, and blood pressure is 88/58 mm Hg. Examination shows scattered petechiae and ecchymoses on the trunk and lower extremities. There is decreased range of motion of the neck. Cerebrospinal fluid analysis shows a cell count of 1,600/μL (80% neutrophils) and a lactate concentration of 5.1 mmol/L. Which of the following is most likely to have prevented this patient's condition?
Polysaccharide conjugate vaccine
Neisseria meningitidis is one of the most common causes of bacterial meningitis in children and young adults in the US. This patient is at high risk because crowded living conditions (e.g., college dormitories, military barracks, etc.) facilitate the spread of N. meningitidis. Meningococcal meningitis can be prevented by meningococcal vaccination. The meningococcal ACWY vaccine, a polysaccharide conjugate vaccine, is usually given at 11 or 12 years of age with a booster dose at age 16 years. For individuals 10–25 years of age with risk factors for invasive meningococcal disease, the meningococcal B vaccine is also recommended. The pentavalent meningococcal vaccine can be considered for individuals 10–25 years of age in whom both meningitis ACWY and meningitis B vaccination are indicated at the same visit. Inactivated whole-cell vaccineInactivated whole-cell vaccines are used in the prevention of, for example, polio (Salk vaccine), hepatitis A, and rabies. Rabies can cause encephalitis, which can present with symptoms similar to those seen in this patient (fever, headache, and lethargy). However, hydrophobia (a pathognomonic feature of rabies) would also be expected. In addition, CSF analysis of rabies would be expected to show a cell count of 5–30/μL instead of the cell count of 1,600/μL seen here. Lastly, rabies is transmitted through the bite of a rabid animal; no such history is given.
An inactivated virus vaccine is available for tick-borne encephalitis, which can present with symptoms similar to those of meningococcal meningitis (e.g., fever, headache, and lethargy). However, this disease is endemic only in Eastern Europe and Asia, and, even in endemic areas, the vaccine is only given to individuals with extensive outdoor exposure. Live attenuated vaccine
Live attenuated vaccines include the MMR vaccine, varicella vaccine, and intranasal influenza vaccine. Mumps and varicella can cause viral meningitis and measles can cause viral encephalitis, which are both associated with headache. However, in viral meningitis or encephalitis, CSF analysis would be expected to show a cell count of < 500/μL with a lymphocytic predominance instead of the cell count of 1600/μL with granulocytosis seen here. In addition, the severity of the patient's symptoms is more consistent with a bacterial etiology. Intravenous vancomycinIntravenous vancomycin, in combination with a third-generation cephalosporin, is appropriate for covering gram-positive bacteria as part of the empiric treatment for community-acquired bacterial meningitis in otherwise healthy patients between the ages of 1 month and 50 years. However, it is not used as a prophylactic measure against bacterial meningitis; even if it were, vancomycin alone would not prevent meningitis caused by N. meningitidis, a gram-negative coccus. Erythromycin therapy
Erythromycin therapy can be used as diphtheria prophylaxis for individuals in close contact with infected patients. Although diphtheria can cause fever, it usually also presents with sore throat and a greyish-white pharynx rather than with neck stiffness and photophobia. Doxycycline therapy
Doxycycline can be administered prophylactically to individuals traveling to malaria-endemic areas. Malaria typically causes a high fever with weakness, jaundice, and malaise. In the case of cerebral malaria, patients may present with confusion, delirium, and seizures. This patient's symptoms of neck stiffness, photophobia, and petechiae with abnormal CSF findings are much more consistent with a presentation of meningococcal meningitis.
Doxycycline is also used for the treatment, not prophylaxis, of Rocky Mountain Spotted Fever (RMSF), which can present with fever, hypotension, headache, myalgias, neck stiffness and a petechial rash. However, CSF would be expected to show a cell count of <100/μL instead of the cell count of 1,600/μL seen here. Furthermore, RMSF is transmitted by tick bite; no such history of tick bite is provided for the patient, and she is less likely to have had a tick bite since she has not recently traveled outside of the large urban area where she attends college. (Most tick bites, but not all, occur in the countryside.) Fluconazole therapy
Fluconazole can be used prophylactically to prevent cryptococcal meningitis. This patient has many characteristic symptoms of meningitis, including neck stiffness, photophobia, and fever. However, cryptococcal meningitis is highly unlikely in immunocompetent patients. In addition, the symptoms of cryptococcal meningitis typically worsen over the course of 1–2 weeks, not within hours. Finally, CSF analysis in cryptococcal meningitis would be expected to show a cell count of 20–200/μL with a lymphocytic predominance, instead of the cell count of 1,600/μL with granulocytosis seen here. Toxoid vaccine
Toxoid vaccines are used to prevent tetanus and diphtheria. Although these diseases could explain some of this patient's symptoms (tetanus causes neck stiffness and diphtheria causes fever), they would not explain her headache, photophobia, and petechial/ecchymotic rash, all of which are suggestive of meningococcal meningitis.
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