Comparing cytomegalovirus diagnostics by cell culture and quantitative nucleic acid testing in broncho‐alveolar lavage fluids

Abstract Many clinical laboratories have replaced virus isolation in cell‐culture (VIC) for cytomegalovirus (CMV) by quantitative‐nucleic‐acid testing (QNAT), rendering clinically relevant CMV‐replication difficult to distinguish from CMV‐shedding or latent infection. We compared direct VIC in 1109 consecutive bronchoalveolar lavage fluids (BALFs) and a well‐validated CMV‐QNAT (Basel‐CMV‐UL111a‐77bp). In the retrospective Group 1 ( N = 694) and Group 2 ( N = 303), CMV‐QNAT was performed within 48 h from 2‐fold and 10‐fold concentrated total nucleic acid (TNA) eluates, respectively. In Group 3 ( N = 112), 2‐fold and 10‐fold concentrated TNA eluates were prospectively analyzed in parallel to VIC. CMV was detected by VIC in 79 of 694 (11%) and 26 of 303 (9%) of Groups 1 and 2, but in 114 of 694 (16%) and 57 of 303 (17%) by CMV‐QNAT, respectively. Median CMV loads were significantly higher in VIC‐positive than in VIC‐negative BALF. The likelihood for CMV detection by VIC was 85% for BALF CMV‐ loads >4 log 10 copies/ml. In the prospective Group 3, CMV was detected by VIC in 10 of 112 (9%), and in 14 of 112 (13%) and 20 of 112 (18%) by CMV‐QNAT, when using 2‐fold and 10‐fold concentrated TNA eluates, respectively. Notably, CMV was undetectable by CMV‐QNAT in 10 VIC‐positive cases of Groups 1 and 2, but in none of Group 3. We conclude that CMV‐QNAT can be adopted to BALF diagnostics but requires several careful steps in validation. CMV‐QNAT loads >10 000 copies/ml in BALF may indicate significant CMV replication as defined by VIC, if short shipment and processing procedures can be guaranteed. Discordance of detecting CMV in time‐matched plasma samples emphasises the role of local pulmonary CMV replication, for which histopathology remains the gold standard of proven CMV pneumonia.