In Reply: The data presented by Dr Jagger and
colleagues suggest the rate of HCV transmission following percutaneous occupational
exposure may be lower than previously recognized. It is difficult for us to
fully evaluate several of the studies they cite, because most were not published
in English. Still, heterogeneity in reported transmission risk is not surprising
since so many factors influence transmission,such as the number of virions
in the inoculum and the susceptibility of the exposed tissues. Available data
suggest that virions must penetrate skin and that larger inocula are more
infectious, as would be expected with exposure to hollow-bore needles containing
blood from persons with a high serum HCV RNA level. Consequently, the overall
risk of transmission from various investigations will vary according to the
nature of the exposures studied. To a lesser extent, differences in ascertainment
of HCV exposure and infection in studies of HCWs may also affect estimates
of transmission risk. It is probably most useful to consider transmission
risk according to at least 3 factors: whether the exposure was (1) via mucous
membrane, intact skin, or percutaneous; (2) from a solid-bore or a hollow-bore
needle, or (3) from blood with high, low, or undetectable HCV RNA levels.
Further research is clearly needed to provide precise estimates in each of
these categories. In the meantime, as Jagger et al point out, HCWs with all
but percutaneous exposure to hollow-bore needles contaminated with HCV RNA–containing
blood (or other deep inoculations) can be reassured that the risk of HCV infection
is very low.