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Pneumocystis jirovecii is the fungus that causes Pneumocystis pneumonia (PCP). Without prophylaxis, PCP may occur in up to 10% of heart-transplant recipients (HTR). Although the fungus has not been cultured, the reservoir is presumed to be humans, and airborne transmission has been hypothesized. Standard prophylaxis is trimethoprim-sulfamethoxazole (TMP-SMX), but atovaquone (ATV) is used in those who are intolerant of TMP-SMX or who have renal dysfunction.
Between March and September 2015, seven cases of PCP were noted among 124 HTR at one hospital. Six of the seven were receiving ATV for prophylaxis and the other was on no prophylaxis. In those on ATV, serum levels were not significantly different in those with PCP compared to those without PCP. However, the risk for PCP among the 10 patients on ATV was significantly higher than for the 24 patients on TMP-SMX. The same multilocus genotype was found in 5 of the 7 patients with PCP as well as 2 of 3 HTR found to have nasopharyngeal colonization. Moreover, a transmission map suggested that either of two patients could have been the index case for transmitting Pneumocystis in the outpatient clinic. The more likely index patient had HIV infection. The outbreak was stopped by starting TMP-SMX in all HTR attending the clinic.
Vindrios W et al. Outbreak of Pneumocystis jirovecii infection among heart transplant recipients: Molecular investigation and management of an interhuman transmission. Clin Infect Dis 2017 May 26; 65:1120. (http://dx.doi.org/10.1093/cid/cix495)
Comment
These findings raise three important points. First, they strongly suggest the occurrence of airborne transmission of Pneumocystis in immunocompromised patients in an outpatient setting. Second, they demonstrate the utility of molecular methods in defining the transmission. Finally, they show that ATV is likely an inferior agent to TMP-SMX for PCP prophylaxis. As the authors note, based on these and other results, it is certainly reasonable to place hospitalized patients with PCP in a single room and perhaps to ask them to wear a surgical mask in an outpatient clinic setting.