A 4-year-old male is brought to your office because of a circular reddish rash under his armpit. The child has been afebrile and has had no other systemic symptoms. The rash is not pruritic. The child's parents state that they have recently returned from a vacation in Massachusetts on Cape Cod and that a small tick had been removed from the same area where the rash is now. The only abnormality on the examination is the circular, flat, erythematous rash that is about $6 \mathrm{~cm}$ in diameter and is not tender. The appropriate next step in treating this patient is to

A 4-year-old male is brought to your office because of a circular reddish rash under his armpit. The child has been afebrile and has had no other systemic symptoms. The rash is not pruritic. The child's parents state that they have recently returned from a vacation in Massachusetts on Cape Cod and that a small tick had been removed from the same area where the rash is now. The only abnormality on the examination is the circular, flat, erythematous rash that is about $6 \mathrm{~cm}$ in diameter and is not tender. The appropriate next step in treating this patient is to

Which of the following diagnostic tests is LEAST useful in establishing a diagnosis of mesenteric adenitis due to Yersinia pseudotuberculosis?

The 12-year-old son of diplomat parents presents with crampy abdominal pain, fever, migratory arthralgias, and hepatosplenomegaly. During the past 5 years, his family has lived in the Philippines, Kampuchea, Senegal, and Mali. Ultrasound examination of his abdomen shows periportal fibrosis consistent with schistosomiasis. His kidneys and bladder are normal. Which of the following schistosome species is UNLIKELY to be the cause of his illness?

Pyelonephritis is a frequent cause of fever in young infants. All of the following infants have an increased risk of urinary tract infections EXCEPT

The drug of choice for empirical treatment of indwelling line and prosthesis infections caused by coagulase-negative staphylococci is