Hepatitis C virus dried on inanimate surfaces can remain infectious for up to six weeks

Dried spots of blood contaminated with hepatitis C virus (HCV) can remain infectious for up to six weeks at normal room temperatures, research published in the online edition of the Journal of Infectious Diseases shows. Commercially available antiseptics reduced the infectivity of the blood spots, but only when used at recommended concentrations.

“We observed that HCVcc [cell culture] could maintain infectivity for up to 6 weeks at 4^o and 22^o C,” write the authors. “Commercially available antiseptics reduced the infectivity of HCV on surfaces only when used at the recommended concentrations, but not when further diluted.”

The investigators believe their findings could explain hospital-acquired HCV infections in individuals who have not undergone surgery or received blood products, and also the ongoing HCV epidemic among injecting drug users.

HCV is a blood-borne virus. Injecting drug use is a well-known risk factor, and a large number of individuals were infected with HCV after receiving blood or blood products. But research suggests that hospital-acquired infections are occurring among patients who did not receive blood/blood products or undergo an invasive procedure. Investigators from Yale University hypothesised that this was due to contact with infectious quantities of HCV in minute dried blood spots on inanimate surfaces and objects.

They therefore performed a series of experiments to establish the circumstances in which healthcare workers or patients could come into contact with infectious HCV dried on surfaces. The investigators believe theirs is the first study to “closely simulate” the conditions leading to hospital-acquired HCV infection.

Blood spots with potential infectious HCV titres were dried onto plates and stored at temperatures of 4^oC, 22^oC and 37^oC for up to six weeks. The authors also examined the effect of three commercially available antiseptics – bleach, cavicide and ethanol – on the infectivity of the HCV-contaminated dried blood spots.

Using a testing assay with a detection limit of 1000 RLA, potentially infectious HCV was recovered from dried blood spots stored at 37^oC for up to seven days. At temperatures of 4^oC and 22^oC, replicating HCV was recovered for up to six weeks of storage. The infectivity of the dried spots declined sharply during the first two weeks of storage at these temperatures. Nevertheless, potentially infectious quantities of HCV – albeit at low levels – continued to be recovered for up to six weeks.

Blood spots with higher HCV titres (10⁶ infectious units/ml) were also tested. Almost all spots stored at 4^oC and 22^oC remained potentially infectious after three weeks of storage. After ten days of storage, 100% of spots stored at 37^oC also contained replicating HCV.

But commercially available antiseptics were highly effective against the HCV-contaminated blood spots. One minute of exposure to bleach (diluted to a ratio of 1:10) was 100% effective, whereas cavicide at a similar concentration was 94% effective and ethanol (70%) eliminated HCV in 87% of blood spots. The effectiveness of these disinfectants was significantly reduced when their concentrations were reduced below recommended levels.

“There are several commercially available antiseptics that are effective against HCV,” write the authors.

They conclude that HCV can remain infectious at room temperatures for up to six weeks, “a biological basis for recent observational studies reporting increasing incidence of nosocomial [hospital-acquired] HCV infections and continued high incidence among people who inject drugs.”