People living with chronic HBV People living with viraemic HCV
Topic:
Hepatitis, burden of disease
Rationale:
This indicator reflects epidemic and service needs, since it serves as numerator or denominator for several other indicators along the result chain and cascade (coverage and impact indicators).
Definition:
• Estimated number of people in the total population (all ages) who are HBsAg positive
• Estimated number of people in the total population (all ages) who are alive and currently viremic i.e people who have been exposed to HCV and are currently have an active infection (anti-HCV(+) and HCV RNA positive)
• Adjusted number of people in the total population (all ages) ever infected with HCV and are currently have an active infection (anti-HCV(+) and HCV RNA positive) any year prior to or in the given year including those cured
Disaggregation:
By country and WHO region
Method of measurement
Routine surveillance data reported by countries.
For HCV, the adjusted number of people living with viraemic HCV includes those with resolved infection (cured or naturally cleared).
Where these data are unavailable, WHO leads a consultative process to produce country-calibrated modelled estimates of number of people who are living with chronic HBV and those living viraemic HCV infection in the reporting year.
Method of estimation:
The PRoGReSs model is used to quantify the annual HBV-infected population by disease stage, sex, and age in a country. The model integrates demographic profiles, vaccination coverage (including timely birth dose and three-dose infant series), prevention measures such as hepatitis B immune globulin (HBIG) and maternal antiviral prophylaxis, HBV diagnosis and treatment schedules, and established HBV epidemiological parameters. Perinatal, early childhood and horizontal transmission are modelled using age-specific hepatitis B surface antigen (HBsAg) prevalence together with available prevention-coverage data.
The disease stages considered in the PRoGReSs model are chronic hepatitis B, compensated cirrhosis, decompensated cirrhosis, hepatocellular carcinoma, and liver transplant .HBV-infected population in each disease stage is further divided into high-viral load (HBsAg-positive with HBV DNA of 20,000 IU/mL or more), low-viral load (HBsAg-positive with HBV DNA of less than 20,000 IU/mL), and treatment responder subpopulations. The population susceptible to HBV is also tracked by age and sex, consisting of uninfected individuals who had never been exposed to HBV and had not been successfully immunized. Those developing a chronic hepatitis B infection are split into low- and high-viral load cases using reported data on respective proportions of high-viral load cases among HBeAg-negative and HBeAg-positive populations. Since the risk for chronic hepatitis B infection largely depends on the age of acquisition of infection, the model begins in 1900 to allow for full flexibility.
Number of people living with viraemic HCV infections are estimated using the Markov/semi-dynamic (disease progression) model . The model employs a natural history framework that follows people with viraemic infection across stages of liver disease, by age and sex, over time using disease progression and mortality (all-cause and liver-related) rates. It incorporates inputs from demographic profiles, HCV diagnosis and treatment initiation schedules, and subsequent cure (sustained virological response, SVR).The model starts with the annual number of acute infections that progressed to chronic HCV (viremic) infection after accounting for spontaneous clearance of the virus.The progression of these new cases is followed along with all chronic infections from prior years. Unless specified, the scope of the model is limited to viraemic, HCV ribonucleic acid (RNA) positive cases. Non-viraemic cases (those exposed to the virus but spontaneously cleared the virus or were treated and cured) are not considered. The number of new cases at each stage of disease (incidence) is calculated annually by multiplying the annual progression rates times the prevalent population (by age and gender) in the previous stage. After one year, new cases are considered prevalent cases (after accounting for mortality and cured).
Method of estimation of global and regional aggregates:
Regional estimates are the sum of the country data in each WHO region.
Preferred data sources:
National population-based surveys in high-burden epidemics, otherwise modelled estimates
Unit of Measure:
Cases
Expected frequency of data dissemination:
Every two years
Expected frequency of data collection:
Continuous at country level reported every two years to WHO
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