Researchers from Australia reported a high rate of hepatitis C virus reinfection and spontaneous clearance of reinfection among injection drug users, suggesting that the patients may have acquired a partial immunity to the virus.
The study included 188 patients with HCV who had injected drugs in the past 6 months. There were nine confirmed HCV reinfections in seven patients and 17 possible reinfections in 16 patients. Blood samples were screened for the virus and positive samples were retested. HCV RNA samples were genotyped; a confirmed reinfection was defined as genetically distinct from the previous infection, and a possible reinfection was an instance in which a genetic distinction could not be made.
During the 5-year study period, the incidence of confirmed HCV reinfection was 28.8 per 100 person-years (95% CI, 15-55.4). The combined incidence of confirmed and possible reinfection was 24.6 per 100 person-years (95% CI, 16.8-36.1). The risk for HCV reinjection in this cohort was approximately twice that of primary infection (HR=1.93; 95% CI, 1.01-3.69), although the risk was not statistically significant once the researchers limited their analyses to confirmed reinfections only (HR=2.45; 95% CI, 0.87-6.86).
Predictors of confirmed and possible HCV reinfection included shorter duration of injection drug use (HR=0.91; 95% CI, 0.83-0.98) and having multiple recent partners who used injection drugs (HR=3.12; 95% CI, 1.08-9).
According to the researchers, the time to spontaneous clearance was shorter in patients with confirmed reinfection (HR=5.34; 95% CI, 1.67-17.03), and confirmed and possible reinfection (HR=3.1; 95% CI, 1.1-8.76) compared with primary infection. However, the researchers noted that 50% of confirmed reinfections and 41% of confirmed or possible reinfections did not spontaneously clear.
"Both the elevated rate of spontaneous clearance in reinfection and the persistence of a considerable proportion of reinfections have implications for our understanding of acquired natural immunity to HCV," the researchers wrote. "The persistence of a large proportion of reinfections also highlights the need for public health campaigns to educate [people who inject drugs] about the ongoing risk of infection after spontaneous HCV clearance, and potentially after successful antiviral treatment."
Disclosure: The researchers report no relevant financial disclosures.