A month old HIV positive child following URTI developed sudden onset of breathlessness. The chest x-ray shows hyperinflation. The O2 saturation was greater than 90%. The treatment of choice is –
**Core Concept**
Pneumocystis jirovecii pneumonia (PCP) is a common opportunistic infection in HIV-infected individuals, particularly in those with severe immunocompromise. PCP can present with non-specific respiratory symptoms, including cough, dyspnea, and tachypnea.
**Why the Correct Answer is Right**
In this clinical scenario, the presentation of sudden onset breathlessness in an HIV-positive child following a URTI, along with the chest x-ray showing hyperinflation, is highly suggestive of PCP. The O2 saturation greater than 90% indicates that the child is not in acute respiratory failure, but rather has a more chronic or subacute presentation. The treatment of choice for PCP is trimethoprim-sulfamethoxazole (TMP-SMX), which acts by inhibiting dihydrofolate reductase, an enzyme essential for the synthesis of tetrahydrofolate in the folic acid pathway.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because ampicillin is not the first-line treatment for PCP. Ampicillin is a beta-lactam antibiotic that acts by inhibiting cell wall synthesis, which is not relevant to the treatment of PCP.
* **Option B:** This option is incorrect because azithromycin is a macrolide antibiotic that is used to treat a variety of bacterial infections, but it is not effective against PCP.
* **Option C:** This option is incorrect because corticosteroids, such as prednisone, can be used in certain cases of PCP to reduce inflammation, but they are not the primary treatment.
**Clinical Pearl / High-Yield Fact**
PCP is a classic opportunistic infection in HIV-infected individuals, particularly in those with CD4 counts <200 cells/μL. The diagnosis of PCP is often made clinically, based on the presence of non-specific respiratory symptoms and a characteristic chest x-ray appearance, rather than by culture or PCR.
**Correct Answer:** C. Prednisone