We appreciate the opportunity to comment on this thoughtful letter regarding the U.S. Preventive Services Task Force's grade I recommendation for screening high-risk individuals for HCV infection. It is important to begin with a correction: A grade I recommendation is not a recommendation against screening, as Drs. Rich, Taylor, and Allen suggest. The Task Force recommends against a service only when it finds at least fair evidence that the service is ineffective or that the harms of providing the service outweigh the benefits (such services are then given a grade D recommendation). Rather, when assigning a grade I recommendation, the Task Force concludes that it cannot recommend for or against routinely offering a service because evidence of the service's effectiveness is lacking, of poor quality, or conflicting and the balance of benefits and harms cannot be determined (1).

Such was the case when the Task Force considered the evidence for screening high-risk individuals for HCV infection. There is evidence that available screening tests can accurately identify HCV infection and that treatment reduces the intermediate outcome of viral load. However, the connection between the treatment of HCV infection detected through screening and the long-term health outcomes is not well substantiated by the evidence. Similarly, there is no direct evidence that behavioral interventions in HCV-positive patients either promote behaviors that reduce the transmission of HCV to others or reduce behaviors that put the patients' own health at risk. Extrapolating from the literature on screening and treatment for other diseases creates the potential for error and serious consequences.

It is essential that the Task Force adhere to its established rules of evidence (1) in making recommendations. There are many compelling reasons to screen high-risk persons for HCV infection (for example, as a public health strategy for conducting surveillance and public awareness programs). However, on the basis of the available evidence, the Task Force could not recommend for or against such screening in the primary care setting because the available evidence does not indicate that it will improve health outcomes.