Epidemiology of hepatitis C virus infection

Abstracts

Hepatitis C is a major cause of chronic liver disease worldwide. There is a significant variation in the prevalence of hepatitis C virus (HCV) infection according to the geographic region studied. These discrepancies reflect not only distinct epidemiological characteristics among the populations, but also differences in the methodologies used for the estimates. Despite scarce data, estimates indicate that Brazil is a country with an intermediate prevalence of HCV infection, ranging from 1% to 2%. The most important risk factors for HCV acquisition include injection drug use, blood product transfusion, organ transplantation, hemodialysis, occupational injury, sexual transmission and vertical transmission. Because there is no vaccine and no post-exposure prophylaxis for HCV, the focus of primary prevention efforts should be identification and removal of the risk factors. In this article we review literature regarding the prevalence of HCV infection, particularly in Brazil. In addition, we discuss the pattern of HCV infection according to the age groups and risk factors for HCV acquisition.

Hepatitis C; epidemiology; disease transmission, infectious; prevalence; risk factors

A hepatite C é uma das principais causas de doença hepática crônica em todo o mundo. Existe grande variação na prevalência da infecção pelo vírus da hepatite C (HCV) de acordo com a região geográfica estudada, refletindo não só características epidemiológicas distintas entre as populações, mas diferenças nas metodologias utilizadas para a realização das estimativas. Apesar dos dados escassos, estimativas indicam que o Brasil é um país com prevalência intermediária, variando entre 1% e 2%. Os principais fatores de risco para a infecção pelo HCV são a transfusão de hemoderivados de doadores não rastreados com anti-HCV, uso de drogas intravenosas, transplante de órgãos, hemodiálise, transmissão vertical, exposição sexual e ocupacional. Pela ausência de vacina ou profilaxia pós-exposição eficaz, o foco principal da prevenção está no reconhecimento e controle desses fatores de risco. Neste artigo será feita uma revisão da literatura com enfoque na prevalência da hepatite C, especialmente no Brasil. Além disso, serão discutidos aspectos relacionados à distribuição da infecção pelo HCV de acordo com as faixas etárias e também os principais fatores de risco para a hepatite C.

Hepatite C; epidemiologia; transmissão de doença infecciosa; prevalência; fatores de risco

REVIEW ARTICLE

^IPharmacist and Biochemist from Universidade do Sul de Santa Catarina - UNISUL; and Post-Graduate Student in Health Sciences at UNISUL, Tubarão, SC, Brazil

^IIPhD in Gastroenterology and Hepatology from Universidade Federal de São Paulo; Professor of the Health Sciences Post-Graduate Program of UNISUL, Tubarão, SC, Brazil

Corresponding author

ABSTRACT

Hepatitis C is a major cause of chronic liver disease worldwide. There is a significant variation in the prevalence of hepatitis C virus (HCV) infection, according to the geographic region investigated. These discrepancies reflect not only distinct epidemiological characteristics among populations, but also differences in methodologies. Although data are scarce, estimates indicate that, in Brazil, the prevalence of HCV infection is intermediate, ranging from 1% to 2%. The most important risk factors for HCV infection include intravenous drug use, blood product transfusion, organ transplantation, hemodialysis, occupational exposure, sexual transmission, and vertical transmission. Due to lack of vaccine or effective post-exposure prophylaxis, the main focus of prevention is to recognize and control these risk factors. In this article, we review the literature on the prevalence of HCV infection, particularly in Brazil. In addition, we discuss the pattern of HCV infection according to the age groups and risk factors.

Keywords: Hepatitis C; epidemiology; infectious disease transmission; prevalence; risk factors.

Introduction

Since the isolation of complementary DNA of hepatitis C virus (HCV) by Choo et al.¹, in 1989, hepatitis C has been recognized as one of the main causes of chronic liver disease worldwide.

Prevention and control of hepatitis C depend on a complex evaluation of global distribution of HCV infection, determination of its risk factors, and assessment of factors that accelerate disease progression. Moreover, due to the lack of a vaccine or some form of post-exposure prophylaxis, an accurate epidemiological assessment to plan primary prevention actions in any given population is essential².

Search criteria

An exhaustive review of the literature on the epidemiology of hepatitis C was carried out. The Medline and Scielo databank were searched using the following combination of words: hepatitis C; epidemiology; prevalence; risk factors; and transmission. Studies or case reports, correspondences, commentaries, or non-published studies were not included.

Global prevalence

One of the ways of estimating the prevalence of hepatitis C is through seroprevalence studies performed in blood donors. However, since this is a population with specific characteristics, such studies may not accurately represent the real prevalence of disease. This discrepancy has been demonstrated in the North American population, which in the 1990s had an estimated prevalence of HCV infection of 0.6% in studies of blood donors and 1.8% in general population³. Other investigations, such as those in patients with chronic liver disease, should also be carefully interpreted, since those individuals do not adequately represent the total population of a specific area. Although populational studies with representative samples of one or more communities are more appropriate, they are more complex and expensive and may not be accomplished in most regions of the world. Even with these considerations, estimates indicate a global prevalence around 2% to 3%, i.e., between 123 million and 170 million people with HCV infection worldwide^2,4-7.

Although hepatitis C is considered endemic worldwide, there is a high degree of geographical variation in its distribution^2,4-7. In many countries data are missing, and estimates are based on adjusted means for a specific region. Figure 1 shows the estimated prevalence of HCV infection according to geographic region.

The prevalence of HCV infection is low, in the United Kingdom, Scandinavia (0.01% to 0.1%), Americas, Western Europe, Australia, and South Africa (0.2% to 0.5%)⁸. Intermediate prevalence is seen in Eastern Europe, Mediterranean, Middle East, and India⁸. Other countries with intermediate prevalence include Brazil, Eastern Europe, parts of Africa, and Asia^4,8. Egypt has a high prevalence of HCV infection (17% to 26%). besides Hubei, Mongolia, and Pakistan^4,6.

There is only a limited number of studies relating the prevalence of HCV infection at different ages, and they show not only regional but temporal variations that reflect times of HCV transmission increased risk in each region⁶. In these works, at least three distinct epidemiological patterns are observed (Figure 2). The first pattern occurs in countries like USA and Australia with the highest prevalence of HCV in the population between 30 and 39 years of age and lower prevalence in those aged below 20 and above 50 years⁴. In this case, it has been hypothesized that higher rates of transmission had, in the recent past, affected the 10 to 30 years age group⁴. The second pattern, seen in Turkey, Spain, Italy, Japan, and China, the majority of those infected are over the age of 50, which might indicate a greater risk of infection in the distant past, roughly between 40 and 60 years⁴. The third pattern, seen in Egypt, in which an increase in the number of cases with age and, at the same time, a large number of cases in all age groups, indicates an increased risk of transmission in the distant past, which is continuously maintained^2,7. Identification of those prevalence patterns of HCV infection in different age groups probably shows the epidemiologic characteristics specific to each region. Knowledge of the prevalence pattern in different countries and places might allow greater effectiveness of HCV infection detection and control.

Prevalence in Brazil

Brazil is a continental country and, therefore, with large demographic, social, and cultural variations among its different regions. For this reason, studies evaluating the prevalence of HCV in Brazil are scarce and not precise, usually encompassing restrict geographic areas or specific populations, such as blood donors⁹. Reports of several studies have contradictory information, suggesting the need for studies with more appropriate methodology.

A survey by the Brazilian Society of Hepatology showed that out of 1,173,406 blood donors evaluated, 14,527 (1.23%) were positive for anti-HCV. Figure 3 shows the spatial distribution of anti-HCV positivity per state¹⁰. The higher prevalence rates were observed in Northern states (2.12%)¹⁰. On the other hand, the Southern region showed low prevalence of anti-HCV positivity (0.65%). Midwestern, Northeast, and Southeast regions showed intermediate rates (1.04%, 1.19%, and 1.43%, respectively)¹⁰. However, as discussed earlier, the use of a specific group, such as blood donors, limits extrapolation of these estimates for general population.

In 1998, a populational study by Focaccia et al.¹¹, reported a prevalence of anti-HCV positivity of 1.42% in 1049 residents of São Paulo county.¹¹ Higher prevalence was observed in individuals over 30 years of age, with the peak of 3.8% seen in the 50 to 59-year age group¹¹. As mentioned before, the greater prevalence of hepatitis C observed after the age of 50 suggests infection in the distant past and a gradual dislocation among age groups, with a tendency to concentrate most cases among the elderly.

Risk and transmission factors

The investigation of the risk factors for HCV infection can be done by prospective or retrospective studies, and several studies indicate as main risk factors: transfusion of blood and blood products from non-tested blood donors; organ transplantation from infected donors; IV drug use; therapy with injected drugs with contaminated (or not safe) equipment; hemodialysis; occupational exposure to blood; perinatal infection; and sexual transmission^12-16. Moreover, due to the great variety of human activities with potential exposure to blood, several possible biologic transmission models exist, such as tattoo, piercing, barber shop, scarification rituals, circumcision, and acupuncture.

Among the different risk factors, the ones described most often in literature include blood transfusion, IV drug use, and invasive therapies with contaminated (or unsafe) equipment^12,13. However, a significant variation on the importance of each of those factors in disease transmission was observed over time in each region⁷.

Transfusion of blood products

Transfusion of blood and blood products from nontested donors is considered the most important type of transmission. However, after randomization of predonation screening processes, a significant reduction in HCV transmission through blood products transfusion was observed¹⁷. It has been estimated that, between 1960 and 1991, 5% to 15% of blood product receptors were infected with HCV and that, currently, after adoption of screening tests, the risk of infection from blood transfusion is around 0.001% per unit of blood transfused18. Despite this significant reduction observed in the last years, a study performed in the largest blood bank in Santa Catarina demonstrated that the possibility of contamination by HCV is still in the other of one to 13.721 units of blood transfused¹⁹, which is at least 10 times higher than that observed in developed countries¹⁹.

Intravenous drug use

After reduction in HCV transmission by blood products transfusion, sharing contaminated material by IV drug users became the greatest risk factor for transmission of disease. Intravenous drug use was one of the main types of HCV transmission in the last 40 years in countries like the United States and Australia^12,20, being currently the main risk factor in developed countries^12,20. In these countries, IV drug use is responsible for approximately 70% to 80% of HCV contaminations in the last 30 years^12,20.

A study by Thorpe et al. demonstrated that the prevalence of HCV infection among IV drug users has varied from 70% to 90%²¹, and it seems to increase with the time of use^22,23. However, some studies have demonstrated that even the recent users (less than six months) can present rates higher than 75%²¹. In Brazil, statistics are scarce. However, in a study that evaluated the prevalence of anti-HCV in IV drug users in the city of Santos, showed a rate of 75%, comparable to rates reported by most countries.

Medical procedures and nosocomial exposure

Injectable therapies with contaminated (or unsafe) equipment represent another possible form of HCV transmission²⁵. Despite the scarcity of reliable data, it has been estimated that approximately two million individuals are infected annually by this route²⁵. In developing countries, the supply of sterilized material can be inadequate or nonexistent. Moreover, outside of medical centers, injectable therapies might be performed by untrained individuals; therefore, throughout life, a person can received several injections with contaminated material, increasing significantly the accumulate risk of HCV infection²⁵. In Egypt, the country with the higher prevalence of hepatitis C in the world, most individuals were contaminated by reusing glass syringes during national campaigns to treat schistosomiasis between 1960 and 1987²⁶. Similarly, in India, the prevalence of HCV among patients who received several injectable treatments for kala-azar is 31.1%, which is significantly higher than the prevalence observed in general population²⁷.

Patients on hemodialysis have higher prevalence of HCV infection⁵, ranging from 19% to 47.2%¹⁰. Among the factors associated with higher HCV infection rates in hemodialysis patients are the time of dialysis and demographic region⁶, Hepatitis C virus transmission among hemodialysis patients is mainly nosocomial. Possible risk factors include sharing hemodialysis equipment and instruments and the lack of adhesion to standard precaution measures and equipment sterilization²⁸.

Solid organ transplantation

The estimated prevalence of HCV infection in organ transplant recipients is complicated by the influence of immunosuppression on the accuracy of serological tests commonly used. The prevalence of anti-HCV in organ donors, according to studies in cadavers, ranges from 4.2% to 5.1%, depending on the test used²⁹. Recipients from anti- HCV positive donors seem to have elevated seroconversion rates; in a study with patients who received kidney grafts, 35% of recipients from anti-HCV positive donors developed post-transplantation liver disease, and 74% showed evidence of viremia³⁰. Despite these data, evidence is still limited and there is a clear need for further studies to evaluate the impact of organ transplantation in the prevalence of HCV.

Occupational exposure

Needle sticks accidents with percutaneous inoculation is a well-documented HCV transmission, with seroconversion rates after a single percutaneous exposure to known infected material ranging from 3% to 10%^31,32. For this reason, several authors have evaluated the prevalence of HCV in health care professionals. Studies in the early 1990 indicated that the prevalence of HCV infection was three times higher in health care workers than among other professionals³¹. However, other studies indicated a prevalence of 0.7% to 2% among health care workers, which is similar to that of general population. The prevalence of HCV among dentists was 0.7% to 1.7%, and, among oral surgeons, the prevalence was 2% to 9.3%^38,39. A study with orthopedic surgeons who denied the presence of non-occupational risk factors showed a prevalence of less than 1%⁴⁰. Despite these conflicting data, occupational exposure remains a potential risk factor for HCV infection, especially due to the absence of effective post-exposure prophylactic measures in this context.

Vertical transmission

Rates of vertical HCV transmission range from 0% to 20%, with a mean of approximately 5% in most studies^41-43. Risk factors for vertical transmission include elevated maternal viral load, prolonged labor, internal fetal monitoring, and HIV-HCV coinfection^15,44. Coinfected mothers were 3.8 times more prone to transmit HCV to the fetus⁴². Breast feeding did not contribute significantly to HCV transmission⁴³.

Sexual transmission

The risk associated with sexually transmitted HCV is not yet fully understood⁵, and this risk factor is one of the most controversial in the epidemiology of hepatitis C among different results in different studies^45,46. A higher prevalence of HCV infection has been observed among patients treated in clinics specialized in sexually transmitted diseases, among prostitutes and their partners and among patients with HIV-HCV coinfection^47-52,54.

Other risk factors related to sexual behavior seem to contribute for the higher transmission rate of HCV, including: higher number of sexual partners⁴⁶, presence of other sexually transmitted diseases, such as trichomoniasis, HIV/AIDS, syphilis, and Chlamydia,^47,48 low use of condoms^46,53, traumatic sexual experience^46,50,53, and male homosexuality^46,47,53-55. Additionally, male-female transmission seem to be easier than female-male transmission⁵⁶.

Despite this evidence, studies with monogamous couples demonstrated low risk of sexual transmission⁵⁵. Moreover, the possibility of intrafamilial transmission by sharing personal hygiene material or occasional exposure to contaminated blood hinders interpretation of studies assessing sexual transmission of HCV^57,58.

Conclusion

Currently, hepatitis C is one of the most common causes of chronic liver disease worldwide. Evidence suggests that most of the cases in Brazil affect individuals over 50 years of age. However, with the significant reduction in blood products transfusion-related transmission, the role of sharing contaminated material by IV drug users has been increasing and it can be responsible for a significant number of cases, especially among youngsters. Studies with proper methodology in order to establish the prevalence of hepatitis C as well as the risk factors for contracting the disease in the Brazilian population are needed to correctly implement control measures and resource allocation against HCV infection.

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Epidemiology of hepatitis C virus infection

Tatiana Martins^I; Janaína Luz Narciso-Schiavon^II; Leonardo de Lucca Schiavon^II

Publication Dates

• Publication in this collection
  25 Feb 2011
• Date of issue
  Feb 2011

History

• Accepted
  24 Oct 2010
• Received
  07 July 2010