Analysis of mixed infections by multiple genotypes of human cytomegalovirus in immunocompromised patients.

Human cytomegalovirus (HCMV) is a significant cause of morbidity and mortality in immunocompromised patients. The present study was carried out to determine the frequency of occurrence of multiple genotypes of HCMV in immunocompromised patients, to determine if there is any discrepancy in identification of mixed infections by multiple genotypes in paired clinical specimens obtained from patients and to determine the significance of viral load differences between patients infected with single and multiple genotypes. One hundred clinical specimens from 75 patients were included in the study. Real-time PCR; Multiplex PCR and PCR-based RFLP were applied for the determination of viral load and genotyping of HCMV, respectively. Out of the 75 patients, 36 (48%) carried multiple genotypes. Discrepancy with regard to detection of genotypes were found in 17/25 patients whose paired clinical specimens were analyzed. Mixed genotypes were found more often in peripheral blood than urine or intraocular fluids collected from the same patient. There was a statistically significant difference between the median viral loads of clinical specimens carrying single genotypes and multiple genotypes. Mixed infections with multiple genotypes were found predominantly in the leukocyte fraction of peripheral blood specimens. The detection of mixed infections by multiple genotypes in the hypervariable regions of HCMV can be a surrogate marker of an increase in viral load.