Objectives: Despite an abundance of epidemiological evidence for horizontal transmission of hepatitis B virus (HBV), the transmission route remains to be fully elucidated. In a new approach, we evaluated quantitative HBV DNA content in serum, saliva and urine as a first step in exploring possible modes of horizontal transmission.
Methods: In an outpatient setting of an academic hospital, paired serum, saliva and urine samples were collected from 150 chronically infected HBV patients. A validated HBV DNA TaqMan assay was used to quantitatively measure HBV DNA.
Results: Mean log HBV DNA in serum was 5.8 (range, undetectable to 10.0 log HBV DNA) copies/ml, 50% of the patients had an HBV DNA above 10 copies/ml in serum. Mean log HBV DNA level in saliva was 3.2 (range, undetectable to 7.5) copies/ml, 15% had an HBV DNA above 10 copies/ml in saliva. Mean log HBV DNA level in urine was 2.6 (range, undetectable to 5.4) copies/ml and 1% had an HBV DNA above 10 copies/ml in urine. A high, non-linear correlation was shown between HBV DNA in serum and saliva (Spearman's rho 0.82) and between serum and urine (Spearman's rho 0.74).
Conclusions: The significant amounts of HBV DNA found in saliva and urine in chronic HBV patients with high viraemia in serum may have implications for the understanding of hepatitis B epidemiology. The potential infectivity of these body fluids may provide an explanation for the 20% of cases of infection obtained through horizontal transmission for which the origin of infection is yet unknown.