Clinical Scenario:
A 4-month-old infant is brought to the emergency department with fever, progressive cough, poor feeding, and increasing difficulty in breathing for 10 days. The mother was diagnosed with HIV infection during pregnancy but did not receive antiretroviral therapy. The infant has not received cotrimoxazole prophylaxis.
On examination:
- Respiratory rate: 70/min
- Oxygen saturation: 84% on room air
- Mild subcostal retractions
- Bilateral fine crackles with no wheeze
Chest radiograph shows diffuse bilateral interstitial infiltrates.
What is the most likely diagnosis?
A. Cytomegalovirus pneumonia
B. Pneumocystis jirovecii pneumonia
C. Pulmonary tuberculosis
D. Respiratory syncytial virus bronchiolitis
E. Bacterial pneumonia
Correct answer & Explanation:
Correct Answer: B. Pneumocystis jirovecii pneumonia
Explanation
Pneumocystis jirovecii pneumonia (PCP) is the most common life-threatening opportunistic infection in untreated HIV-infected infants. It most commonly presents between 3 and 6 months of age in infants who have acquired HIV vertically and have not received cotrimoxazole prophylaxis.
Typical clinical features include:
- Fever
- Progressive tachypnea
- Nonproductive cough
- Severe hypoxemia
- Minimal auscultatory findings despite marked respiratory distress
- Diffuse bilateral interstitial infiltrates on chest radiography
The combination of young age, untreated maternal HIV infection, absence of cotrimoxazole prophylaxis, severe hypoxemia, and diffuse interstitial infiltrates strongly favors PCP.
Why the other options are incorrect
A. Cytomegalovirus pneumonia
May occur in advanced HIV infection but is less common than PCP in early infancy and usually occurs with other evidence of disseminated CMV disease.
B. Pneumocystis jirovecii pneumonia
Correct. The age, HIV exposure, lack of prophylaxis, progressive respiratory distress, severe hypoxemia, and diffuse interstitial infiltrates are classic.
C. Pulmonary tuberculosis
Usually has a more indolent course and commonly presents with hilar lymphadenopathy, persistent cough, failure to thrive, or focal pulmonary findings rather than diffuse interstitial infiltrates.
D. Respiratory syncytial virus bronchiolitis
Typically presents with wheezing and hyperinflation on chest radiography. Severe hypoxemia with diffuse interstitial infiltrates is less characteristic.
E. Bacterial pneumonia
Usually presents with high fever, toxic appearance, focal chest signs, and lobar or segmental consolidation rather than diffuse bilateral interstitial infiltrates.
Learning Point
Any HIV-exposed infant aged 3–6 months presenting with progressive respiratory distress, severe hypoxemia, and diffuse bilateral interstitial infiltrates should be presumed to have Pneumocystis jirovecii pneumonia until proven otherwise. Treatment is high-dose trimethoprim-sulfamethoxazole (TMP-SMX), with adjunctive corticosteroids indicated in moderate-to-severe disease.
