Correct Answer: D

More than 90% of renal stones are visible on a plain abdominal x-ray, and the majority contain calcium oxalate. Staghorn calculi usually contain magnesium ammonium phosphate (triple phosphate or struvite) and are associated with alkaline urine. This is commonly encountered in chronic urinary tract infections with urea-splitting bacteria. Radiolucent stones often contain urea, which is associated with acidic urine. A small percentage (fewer than 10%) of renal stones contain cystine. The most common cause of calcium stone disease is idiopathic hypercalciuria. Almost half these patients will excrete more than 4 mg of calcium/kg body weight/24 h in the absence of hypercalcemia. Causes of hypercalciuria to be ruled out are sarcoidosis, hyperparathyroidism, and Paget's disease of bone. Idiopathic hypercalciuria is believed to result from either increased GI absorption of calcium, increased calcium resorption from bone, or excessive renal calcium leakage into the urine.

Correct Answer: D

Preterm premature rupture of membranes is a relatively common condition, affecting 318.5% of all pregnancies. It is estimated that 30% of all preterm deliveries result from PPROM. There are multiple etiologies for PPROM, including ascending vaginal infection. Carriers of GBS, bacterial vaginosis, and gonorrhea are all at increased risk for PPROM. Maternal age is not a risk factor, nor is parity, maternal weight, maternal weight gain, or trauma. According to most experts, patients with this condition should be managed in the hospital due to the high risk for amniotic infection, preterm labor, and umbilical cord compression or prolapse. Pulmonary hypoplasia and fetal compression malformations are seen when rupture of membranes occurs in the previable period (less than 24 weeks). The duration of latency (time from rupture of membranes to delivery) varies inversely with gestational age. In other words, at term, labor generally begins within hours. However, even at 28 weeks, up to 90% of patients will go into labor within 1 week.

Correct Answer: B

C. trachomatis is considered an unusual cause of otitis media at any age. N. gonorrhoeae causes conjunctivitis in the newborn. Syphilis and toxoplasmosis cause congenital infections. E. coli is one of the neonatal pathogens that also cause otitis media in neonates. The symptoms of otitis media in newborns are often similar to those of sepsis; they are subtle and nonspecific and may include poor feeding, lethargy, vomiting, or diarrhea. Once the diagnosis is established, the initial therapy should be similar to that for neonatal sepsis, such as parenteral ampicillin and cefotaxime. Under ideal circumstances, the results of cultures obtained by tympanocentesis may then allow further treatment with a more specific antibiotic of low toxicity. Older infants may respond well to oral therapy but require frequent observation.

Correct Answer: C

Hypocalcemia is not a cause of constipation. On the contrary, it increases irritability of nerve cells and may result in diarrhea. Hypothyroidism, lead poisoning, and Hirschsprung disease all may be associated with constipation. Congenital hypothyroidism and Hirschsprung disease (a congenital disorder characterized by regional absence of ganglion cells from the myenteric plexus of the colon) present at birth. Lead poisoning is more common after the child becomes mobile. Functional constipation is the most common cause of constipation at this age. It is usually due to dietary factors.

Correct Answer: D

Knowing the incubation period (average and range) of a pathogen can be important in determining the source of infection in food-borne disease. Knowing what food was eaten on the day of an attack of food poisoning may not help in establishing C. botulinum as the cause of illness, since certain strains of S. aureus cause food-borne disease by the production of enterotoxin. As no time is required after ingestion for the growth of colonies in the infected host, and the toxin affects the vagus nerve in the stomach, the incubation period is under 4 hours. C. perfringens, formerly known as Clostridium welchii, causes food-borne disease, after 824 hours when enterotoxin is released when C. perfringens passes from stomach to intestine. Meat prepared in bulk for consumption at a banquet or in an institution is a possible source. Spores that survive incomplete cooking may start reproducing during cooling and may persist if subsequent rewarming is not completed to a temperature above 60°C (140°F) required to kill the organisms. Salmonella has an incubation time of 1236 hours. It may also survive in meat and other products if cooking is inadequate and heat does not penetrate below the surface of the food. The organisms multiply in the gut of the infected host, and low infective doses may therefore have longer incubation periods