A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 2-week-old boy presents to the pediatrics clinic. The medical records notes a full-term delivery, however, the boy was born with chorioretinitis and swelling and calcifications in his brain secondary to an in utero infection. A drug exists that can be used to prevent infection by the pathogen responsible for this neonate's findings. This drug can also provide protection against infection by what other microorganism?
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A
Mycobacterium tuberculosisIncorrect. TB prophylaxis is isoniazid (or rifampin); TMP-SMX doesn't treat or prevent mycobacterial infection.
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B
Mycobacterium avium complexIncorrect. MAC (Mycobacterium avium complex) prophylaxis is azithromycin (or clarithromycin/rifabutin); TMP-SMX has no significant activity against MAC.
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C
Pneumocystitis jiroveciCorrect. TMP-SMX is used for both toxoplasmosis prevention and PCP (Pneumocystis jirovecii) prophylaxis.
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D
CytomegalovirusIncorrect. CMV prophylaxis is valganciclovir/ganciclovir; TMP-SMX has no anti-CMV activity.
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E
Candida albicansIncorrect. Candida prophylaxis (fluconazole) is used in select immunosuppressed patients but is not the cross-protection of TMP-SMX; TMP-SMX prevents both Toxoplasma and Pneumocystis pneumonia.
↑ Tap an answer to reveal the reasoning
Answer: C. A neonate born with chorioretinitis and intracranial calcifications has congenital toxoplasmosis — the classic triad being chorioretinitis, diffuse (not periventricular) intracranial calcifications, and hydrocephalus. Caused by Toxoplasma gondii (typically from maternal exposure to undercooked meat or cat-feces oocysts during pregnancy).
The drug used to prevent toxoplasmosis (and for prophylaxis in HIV patients with CD4 <100) is trimethoprim-sulfamethoxazole (TMP-SMX). TMP-SMX also provides prophylaxis against Pneumocystis jirovecii pneumonia (PCP) — used as primary prophylaxis in HIV patients with CD4 <200, in solid-organ transplant recipients, and after allogeneic stem cell transplant. So the drug used for one indication conveniently protects against both pathogens.
Key pearl on TORCH calcifications: 'periventricular calcifications' = CMV; 'diffuse intracranial calcifications' = toxoplasmosis. TMP-SMX prophylaxis dual coverage (Toxo + PCP) is a high-yield USMLE association in HIV patients.
**Why each option:**
**A.** TB prophylaxis is isoniazid (or rifampin); TMP-SMX doesn't treat or prevent mycobacterial infection.
**B.** MAC (Mycobacterium avium complex) prophylaxis is azithromycin (or clarithromycin/rifabutin); TMP-SMX has no significant activity against MAC.
**C.** Correct — TMP-SMX is used for both toxoplasmosis prevention and PCP (Pneumocystis jirovecii) prophylaxis.
**D.** CMV prophylaxis is valganciclovir/ganciclovir; TMP-SMX has no anti-CMV activity.