Background: Detecting high herpes simplex (HSV) viral load in lower respiratory tract samples is reported to be significantly associated with the severity of the illness in critical patients, particularly in patients on mechanical ventilation. It may therefore be of interest to quantify HSV in bronchoalveolar lavage (BAL). Quantitative PCR for HSV is not commonly available in clinical routine. Real-time PCR tests are, however, used commonly and provide semi-quantitative information based on the cycle threshold (Ct).
Objectives: Our objectives were to determine the clinically significant threshold and to study the impact of viral load normalisation in relation to cell quantity in samples using real-time PCR.
Study design: During the period 2011-2012, 59 HSV1 positive BAL were included. HSV viral load was determined by a quantitative real-time PCR (R-gene, Argène BioMérieux, France) and compared to a semi-quantitative real-time PCR (SmartCycler®HerpesSimplex, Cepheid, USA). Viral load normalisation was determined using a real-time PCR targeting a cellular gene (Cc r-gene kit, Argène BioMérieux, France). The significant threshold was determined versus clinical features by statistical analysis (Epiinfo Software v3.5.1 CDC).
Results: A viral load of 10(4) copies/ml of BAL was significantly associated with admission to the intensive care unit (p<0.001), mechanical ventilation (p<0.01) and death (p<0.01), with no influence of viral load normalisation in relation to cell quantity in the sample. This viral load was equivalent to a Ct value of 31 in the semi-quantitative technique.
Conclusions: As semi-quantitative techniques are currently used in many labs, determining this Ct value could be useful for interpreting the clinical advantages of detecting HSV in BAL.
Keywords: BAL; Ct; HSV; HSV viral load; ICU; Intensive care unit; Low respiratory samples; Mechanical ventilation; Semi-quantification; Significant threshold; bronchoalveolar lavage; cycle threshold; herpes simplex virus; intensive care unit; real-time PCR; rtPCR.
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