Why should the hepatitis B infection last more than six months to be regarded as chronic?

Question

"People who test positive for the hepatitis B virus for more than six months (after their first blood test result) are diagnosed as having a chronic infection. This means their immune system was not able to get rid of the hepatitis B virus and it still remains in their blood and liver."

Source: https://www.hepb.org/what-is-hepatitis-b/what-is-hepb/acute-vs-chronic/#:~:text=People%20who%20test%20positive%20for,in%20their%20blood%20and%20liver.

Why should the hepatitis B infection last more than six months to be regarded as chronic? My only guess is that, based on stasticial studies, more than half of the patients that got the infection for more than six months could not ever get rid of it.

Is this right? Is there some explaination to what is progressing in these six months, that led to this? Is this a concept common in other diseases?

Why is it 6 not 8 or 4?

Answer 1

Acute infections of Hepatitis B viruses (actually other types too) tend to be duration limited to 4-8 weeks, though it can last as long as 6 months post-infection in rare cases (1). Chronic infection therefore is diagnosed if after 6 months you can still detect viral antigens in the blood.

I'm not sure on the exact processes going on to switch from acute to chronic, but I think it has to do with integration of the viral DNA into the hepatocytes, which allows immune evasion.

References:

(1): Hoofnagle JH, Di Bisceglie AM. Serologic diagnosis of acute and chronic viral hepatitis. Semin Liver Dis. 1991 May;11(2):73-83. doi: 10.1055/s-2008-1040426. PMID: 1909458.