Epidemiology, Diagnosis, and Natural History of Hepatitis B

Sexual

Sexual transmission remains the major mode of spread of HBV in developed countries. Within the United States, heterosexual transmission among adults accounts for 39% and transmission among men having sex with men accounts for 24% of new HBV infections. HBV DNA has been demonstrated in most body fluids, but only blood and semen have been consistently shown to harbor infectious virions. The risk of HBV infection is increased in persons with multiple sexual partners, sexually transmitted diseases, or high-risk sexual behaviors. Transmission can be prevented by vaccination of sex partners and by incorporating safe sex practices in individuals with multiple partners.

Percutaneous

Percutaneous inoculation of blood or body fluids also plays a major role in the transmission of hepatitis B infection. Injection drug use accounts for 16% of new HBV infections in the United States. The reuse of contaminated needles for tattoos, acupuncture, and ear piercing also provides opportunities for percutaneous transmission. In endemic areas, horizontal transmission among children may result from close bodily contact, leading to transfer of the virus across minor skin breaks and mucous membranes. Because HBV remains stable for up to 7 days outside the human body, transmission via contaminated environmental surfaces and daily articles, such as toothbrushes, razors, eating utensils, or toys, may be possible.

Perinatal

The risk of maternal-infant transmission is related to the HBeAg and HBV DNA status of the mother. Perinatal transmission of HBV infection is rare in countries where universal vaccination of newborns is implemented. In the absence of prophylaxis, the risk of perinatal transmission is between 85% and 90% for infants born to HBeAg-positive mothers and 30% for infants born to HBeAg-negative mothers. Maternal serum HBV DNA levels have also been shown to correlate with the risk of transmission. Implementing antiviral therapy in the 3 ^rd trimester of pregnancy to reduce viral load in carrier mothers has been efficacious in reducing perinatal transmission rates. Maternal-infant transmission takes place at the time of delivery via maternal-fetal transfusion or through exposure to maternal blood during passage through the birth canal. Intrauterine transmission is uncommon. Transmission may also occur postnatally through intimate mother-baby contact. This timing of transmission explains the high efficacy of passive-active immunization of newborns. Cesarean section has not been shown to eliminate the risk of perinatal infection and should not be routinely recommended for carrier mothers. Although HBsAg can be detected in breast milk, there is no evidence that HBV infection can be transmitted by breastfeeding. The risk of transmission during amniocentesis is low.

Healthcare Associated

Hepatitis B virus is the most commonly transmitted blood-borne virus in the healthcare setting. HBV infection from blood transfusion is a rare occurrence in the present day. In the United States, both HBsAg and hepatitis B core antibody (anti-HBc) are used for blood donor screening. The risk of transfusion-related hepatitis B from blood donors who test negative for HBsAg and anti-HBc is estimated to be 1 in 63,000. In some countries, blood donors are also screened for HBV DNA. Addition of nucleic acid testing (NAT) will detect a small number of donors that may be associated with risk of transmitting HBV infection. NAT has been implemented in some countries, including the United States. A study of 12.8 million donations screened between 2009 and 2011 in the United States found that addition of minipool nucleic acid testing decreased residual risk of post-transfusion hepatitis B from between 1 : 592,000 and 1 : 754,000 to between 1 : 765,000 and 1 : 1,006,000, comparable to that for HIV or HCV. The cost-effectiveness and overall impact on improving blood safety by the addition of NAT vary depending on the prevalence of HBV infection in the country of study.

Another healthcare-associated risk factor for HBV infection is hemodialysis. Patients on hemodialysis may be infected through blood transfusions, contamination of dialysis machines or equipment, as well as interpersonal horizontal transmission in the dialysis units. Improved infection control and the availability of vaccines have markedly reduced the incidence of HBV infection among hemodialysis patients in the United States. In the Western world, including the United States, all hemodialysis patients are vaccinated usually with double-dose HBV vaccine. Hepatitis B surface antibody (anti-HBs) titers are monitored annually and boosters are given if the anti-HBs titer drops to less than 10 mIU/mL.

Patients undergoing solid-organ transplantation are another population at risk for HBV infection. Organ donors are routinely screened for HBsAg. The role of anti-HBc screening in organ donors is uncertain due to the potential for false-positive results and the uncertainty about the infectivity of organs from donors who are HBsAg negative but anti-HBc positive. Declining donations from HBsAg-negative, anti-HBc-positive persons could result in the loss of up to 5% of donors in low-endemic areas and more than 50% of donors in high-endemic areas. The likelihood of transmission from HBsAg-negative, anti-HBc-positive donors is very low for recipients of nonhepatic organs such as kidneys and negligible for avascular tissue such as cornea, but may be as high as 80% in liver recipients. The risk of transmission is related to the anti-HBs status of the recipient. Antiviral prophylaxis significantly reduces the rate of transmission of HBV infection to liver transplant recipients. The role of antiviral prophylaxis in non–liver transplant recipients is less clear, though some guidelines recommend up to 1 year of antiviral therapy in this setting.

Healthcare-associated HBV infection can occur from patients to healthcare workers and from healthcare workers to patients, though the latter is thought to only rarely occur. Infection in these settings generally occurs via contaminated instruments or accidental needlestick injuries. In many countries, proof of immunity is required of all medical staff performing invasive procedures. The Centers for Disease Control and Prevention (CDC) in the United States recommends adherence to standard precautions for prevention of transmission of infectious diseases, screening healthcare providers at increased risk for infection and those performing exposure prone procedures for HBV infection, and vaccinating those who are seronegative. For healthcare workers with chronic HBV infection who perform exposure-prone procedures, the CDC recommends counseling on measures to prevent transmission, antiviral therapy for those with high levels of HBV DNA, and regular monitoring to ensure HBV DNA levels remain suppressed. In the event of an exposure, the HBsAg status of the source should be determined and the vaccination and hepatitis B surface antibody (anti-HBs) status of the exposed individual should be assessed. This information will guide the need for hepatitis B immune globulin and/or HBV vaccination.