A boy with fever, headache and neck pain that developed over

A 3-year-old boy is brought by his father to the Emergency Department with fever, headache and neck pain that developed over the past several hours. The father states he is not the birth father, and that he and his wife adopted the boy at 18 months of age after his birth mother abandoned him. Physical examination reveals a lethargic male with a temperature of 39.7 C (103.5 F). There is photophobia, and mildly injected conjunctiva are appreciated. Pupils are equal and reactive and funduscopic examination is unremarkable. The patient has neck stiffness with a positive Kernig's sign. A complete blood count reveals a leukocyte count of 24,000/mm3 with 64 segmented neutrophils and 25 bands. A lumbar puncture is performed that reveals elevated CSF pressure, decreased glucose, and elevated protein. A Gram's stain shows gram-negative pleomorphic rods. There is no growth on blood agar. Growth on chocolate agar reveals white colonies. Which of the following is the most likely pathogen?

A. Haemophilus ducreyi

B. Haemophilus influenzae type b

C. Neisseria meningitidis

D. Listeria monocytogenes

E. Streptococcus pneumoniae

B. Haemophilus influenzae type b

Explanation:

Haemophilus influenzae is now a rare cause of meningitis in children since development of the Haemophilus influenzae type b (Hib) vaccine. The case reveals a questionable immunization history, thus making this patient susceptible to H. influenzae type b. Kernig's sign is elicited by placing the patient in a supine position, flexing the leg at the hip to 90 degrees and then straightening the knee to elicit pain in the back or posterior thigh as predictive evidence of meningitis. Laboratory and CSF data support a bacterial etiology, and Gram's stain with growth on chocolate agar confirms the diagnosis of Haemophilus influenzae as the causative agent.

Haemophilus ducreyi(choice A) is the causative agent for chancroid (soft chancre). Neisseria meningitidis(choice C) is a gram-negative diplococcus that also can grow on chocolate agar, but grows best on modified Thayer-Martin media. Meningococcal meningitis classically presents with a petechial rash.

Streptococcus pneumoniae(choice E) and Listeria monocytogenes(choice D) are both organisms that cause meningitis. Both, however, are gram-positive. Listeria monocytogenes is predominantly seen as a cause of neonatal meningitis.