For some people, hepatitis B is a short illness, but for others, it can become long term or chronic and lead to serious liver problems, including cirrhosis and liver cancer. Now, new research finds the risk of liver cancer persists even after the virus is cleared, suggesting people who have had the illness should continue to be monitored.

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Chronic infection with hepatitis B can lead to serious liver problems, including cirrhosis and liver cancer.

The new study - by researchers from the Centers for Disease Control and Prevention (CDC) and the Alaska Native Tribal Health Consortium, both in Anchorage, AK - is published in the journal Alimentary Pharmacology & Therapeutics.

Hepatitis B is a liver infection caused by the Hepatitis B virus (HBV), which spreads when body fluids from an infected person enter the body of another person, such as during sex, from sharing needles and other injecting equipment and from mother to baby at birth.

According to CDC, the risk for chronic infection with HBV is age-related; 90 percent of infected babies become chronically infected, compared with only 2-6 percent of adults.

Since 1991, when a national strategy to eliminate HBV infection was introduced in the US, and when routine vaccination of children was first recommended, the rate of new HBV infections has fallen by around 82 percent.

The CDC estimate that in 2013, the number of people in the United States who were newly infected with HBV was 19,764, with rates highest among adults, particularly men aged 25-44 years.

But the number of Americans living with chronic infection is much bigger; the CDC estimate around 700,000-1.4 million people in the United States have chronic HBV infection, and an estimated 2,000-4,000 die of the condition every year.

Around 25 percent of people who become chronically infected as children, and 15 percent who become chronically infected as adults die prematurely from cirrhosis or liver cancer, and in most cases, they experience no symptoms until these serious diseases occur.

Globally, around 240 million people are living with chronic HBV, and an estimated 786,000 die from HBV-related liver disease each year.

Clearance of HBV appears not to reduce liver cancer risk

For their study, the researchers selected participants from a group of 1,346 Alaska-Native patients with chronic HBV infection who were followed during 1982-2013.

They selected 238 patients whose chronic HBV infection resolved during the follow-up and matched them to 435 patients who remained infected (the controls). The patients were matched by age, gender and HBV strain.

The team found that clearance of HBV appeared to make no difference to the risk of developing liver cancer.

The researchers note while we do not know why HBV clearance appears not to affect risk of liver cancer, they suggest it is likely due to a number of factors.

One reason, for instance, could be the integration of HBV DNA into the genome of liver cells, which occurs early in infection, and can persist after traces of the virus clear from the bloodstream.

The authors note that a "substantial proportion" of the case patients in their study had a detectable level of HBV DNA after virus traces (antibodies against the virus) had cleared from the bloodstream.

This raises the possibility that "ongoing low-level HBV DNA replication with continued integration" into the host liver cell contributes to the persistent risk of liver cancer after the virus has cleared from the bloodstream.

Lead author Dr. Prabhu Gounder says:

"Since the risk of liver cancer persists among adults with apparent cure of the infection, they might still need to be followed closely."

Last month, Medical News Today learned of a study done in mice that found a diet that regularly includes broccoli may protect against liver cancer.