If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
A two-week-old male newborn develops fever, lethargy and seizures. The infant was born at term with no obstetric or early postnatal complications. His temperature is 39.1°C (102.4°F), pulse is 140/min, respirations are 30/min, blood pressure is 100/80 mm Hg and oxygen saturation is 98%. Physical examination shows sunken eyes and bulging fontanelles. The patient has a poor suck reflex and is slightly hypotonic. Examination of cerebrospinal fluid (CSF) obtained on lumbar puncture shows a high neutrophil count and gram-positive cocci in chains. Which of the following is characteristic of the most likely causal organism?
A. Alpha-hemolysis
B. Bacitracin sensitivity
C. CAMP test positivity
D. Growth on bile-esculin agar
E. Optochin sensitivity
The correct answer is C.
Kaplan Medical explains why
This two-week old male presents with fever, seizures, hypotonia, and bulging fontanelles. These symptoms and the spinal fluid findings of a high neutrophil count and gram-positive cocci are consistent with meningitis. The leading cause of meningitis in neonates is S. agalactiae, or group B Streptococcus, which displays CAMP test positivity.
Why the other answers are wrong
Choice A. This neonate presents with meningitis, most commonly caused by Streptococcus agalactiae (group B Streptococcus) in this age group and which has CAMP test positivity. Alpha-hemolysis is a characteristic of Streptococcus pneumoniae, which is the most common cause of meningitis in adult patients.
