Distribution of Hepatitis C Virus Genotypes and Viral Load Levels in the U.S.

Estimates of the long-term benefit of antiviral therapy for chronic hepatitis C virus (HCV) infection are influenced by characteristics that affect treatment response, including HCV genotype and baseline viral load. Studies have shown that treatment response rates are lower among patients with genotype 1 and higher HCV RNA levels.

As reported in the August 2006 issue of Gastroenterology, researchers with the Centers for Disease Control and Prevention conducted a study to determine the distribution of genotypes and viral load levels among the HCV positive population in the U.S.

The study included 275 HCV-infected participants in the Third National Health and Nutrition Examination Survey (NHANES), conducted between 1988 and 1994.

Results

The genotype distribution, from most to least common, was as follows:

- 1a (found in 142 patients);
- 1b (73 patients);
- 2b (27 patients);
- 3a (17 patients);
- 2a (8 patients);
- 6 (5 patients);
- 4 (3 patients).

In a weighted analysis of indiiduals with genotypes 1, 2, and 3, genotype 1 predominated in all age groups (75.3%).

By racial/ethnic group, genotype 1 was found in 90.9% of non-Hispanic blacks, 69.6% of non-Hispanic whites, and 71.2% of Mexican Americans.

After adjusting for age and gender, only non-Hispanic black race/ethnicity was independently associated with genotype 1 infection (adjusted odds ratio 4.9; 95% CI 1.9-12.8).

The overall mean HCV RNA level was 2.1 x 106 IU/mL.

53.0% of patients overall and 50.3% of those with genotype 1 had HCV RNA levels above 2 million IU/mL.

Conclusion

In conclusion, the authors wrote, "Persons with chronic hepatitis C in the United States who may require treatment in the foreseeable future are predominantly infected with genotype 1, including a disproportionate number of non-Hispanic blacks." Since genotype 1 HCV responds less well to treatment, they noted, "These features emphasize the need for improved therapies that reduce or eliminate complications from genotype 1 infections."

8/25/06

Reference
O V Nainan, M J Alter, D Moran-Kruszon, and others. Hepatitis C virus genotypes and viral concentrations in participants of a general population survey in the United States. Gastroenterology. 131(2): 478-484. August 2006.