Pneumocystis jirovecii pneumonia (PJP) is a life-threatening opportunistic infection. Prophylaxis is recommended for patients with malignancies and trimethoprim-sulfamethoxazole (TMP-SMX) is the recommended first-line agent. Many paediatric patients receive second-line agents due to perceived adverse reactions from TMP-SMX.

The objective of the study is to determine the risk of PJP in patients receiving TMP-SMX vs. second-line medications for prophylaxis.

We conducted a retrospective, single centre, case-control study of paediatric oncology patients. Cases included children diagnosed with PJP by microscopy between 2000 and 2018 while being treated for a malignancy. Controls were matched by age, oncologic diagnosis, treatment protocol, phase of treatment and oncologic diagnosis date. For each case, up to 5 controls were randomly selected. The index date was the date of the PJP diagnosis for cases and the equivalent dummy date for controls.

Eleven cases with PJP were identified and matched with 50 controls. Six (55%) cases and 42 (84%) controls were on prophylaxis with TMP-SMX. The remaining patients received inhaled pentamidine (3 cases, 4 controls), dapsone (2 cases, 3 controls), or atovaquone (1 control). Myelosuppression was the most common reason to stop TMP-SMX. Cases with PJP were less likely to have been taking TMP-SMX in the 3 months before diagnosis when compared with controls (odds ratio: 0.15, 95% confidence interval: 0.01-0.97, p = 0.02).

TMP-SMX prophylaxis was associated with a lower risk of developing PJP compared with second-line treatments. Although alternate agents may be required in certain situations, efforts should be made to rechallenge with TMP-SMX when possible.