Effect of oral washes on the diagnosis of Pneumocystis carinii pneumonia with a low parasite burden and on detection of organisms in subclinical infections

This study was designed to assess the efficacy of using oral washes (OWs) t o diagnose Pneumocystis carinii pneumonia (PCP) in patients with a low para site burden and to detect cases of subclinical infection. A total of 104 pa ired induced sputum (IS) samples and OWs from 104 HIV-seropositive patients and 32 OWs from immuno-competent healthy controls were studied. All of the control samples were negative. Fifty-two IS specimens were positive for Pn eumocystis carinii, and 26 of these cases were also detected in the OWs usi ng conventional stain or polymerase chain reaction. Twenty-four of the PCP cases had a high or a moderate parasite load and 28 had a low parasite load ; among them, Pneumocystis carinii was detected in the OWs of 15 and 11 cas es, respectively. Fifteen of the 104 IS samples studied belonged to patient s who were asymptomatic carriers or who had a subclinical infection, and Pn eumocystis carinii was detected in the OWs of 4 of these cases. The parasit e was not detected in 37 IS samples and in 74 OWs. The results of this stud y indicate that in patients with a low pulmonary parasite burden, the numbe r of organisms reaching the oral cavity is insufficient for reliable detect ion in OWs. Thus, OWs are less useful than IS samples for detecting Pneumoc ystis carinii in cases of pneumonia in which a low parasite burden and/or s ubclinical infection are present.