Abstract
Background
Blood transfusions carry the risk of transmitting blood-borne infections. In contrast to the situation in the developed world, there is a limited number of studies examining this problem in sub-Saharan Africa. In this study we aimed to calculate the risks of acquiring human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV) infection from units of blood issued by the Gabonese Blood Transfusion Centre between 2009 and 2011.
Materials and methods
All the donations were tested for infectious diseases and the seroconversion incidence rates of HIV, HBV and HCV were calculated. The residual risk of transfusion-associated transmission for each virus was calculated by multiplying the seroconversion rates by the window period expressed in fractions of a year.
Results
The risks of becoming infected with HIV, HCV, and HBV in subjects receiving units of blood from the Gabonese Blood Transfusion Centre were 64.7, 207.94 and 534.53 per million donations, respectively.
Conclusions
This study, which is the first to quantify the true risks of transfusion-transmitted infections in Gabon, reveals and confirms the need to reinforce preventative and screening strategies to improve transfusion safety in sub-Saharan Africa.
Keywords: HIV, HBV, HCV, transfusion-transmitted infections, risk
Introduction
The blood-transmissible character of viruses such as human immunodeficiency virus (HIV), hepatitis B virus (HBV) and hepatitis C virus (HCV) has heightened public concern about the safety of blood transfusions. This is all the more the case in in developing countries in which blood transfusion is still challenging considering the high prevalence of blood-borne pathogens and the difficulties in ensuring a safe blood supply1–5. In Gabon the seroprevalence of HIV, HBV and HCV in the general population is 5.2%6, 11.1%7 and 11.2%8, respectively.
Monitoring the trends in the residual risks of transfusion-transmitted infections or the incidence of transmissible infectious agents in blood donations provides a way not only of evaluate the safety of the blood supply9,10, but also of motivating the introduction of new sensitive screening techniques that will improved early detection of infected individuals11–18.
The National Blood Transfusion Centre (CNTS) of Gabon currently selects blood donors on the basis of a health check questionnaire and serological screening for HIV, HCV and HBV antibodies and surface antigen, a method, which is less sensitive than nucleic acid screening tests (NAT).
Here we present the prevalence of HIV, HCV, and HBV among Gabonese blood donors and the incidence rates of seroconversion among blood donors for these major blood-borne viruses for the period 2009–2011.
Materials and methods
Data analysed and reported here are based on the 2009–2011 CNTS records of blood donors containing donors’ information and the results of the serological screening. All candidate blood donors sign a consent form giving the CNTS the right to use data associated with their donation for epidemiological research studies. The institutional review board at the CNTS approved this study protocol. The routine procedure for selecting donors includes: (i) a physical examination (body-mass index and blood pressure), (ii) a screening questionnaire (donor medical history) and (iii) blood tests for blood-borne pathogens. At the time of the study, screening for transfusion-transmissible infections relied on the use of fourth-generation tests that combine antibody/antigen detection, as recommended by the World Health Organization guidelines11. Briefly, HIV status was assessed using Genscreen ultra HIV Ag-Ab from Bio-rad (Marnes-la-Coquette, France); HCV was assessed using Monolisa HCV Ag-Ab ultra from Bio-rad, and HBV was tested using HbsAg ultra from Bio-rad. If the first test was reactive, to confirm the infection the donor was called back and a supplemental test was done on a newly collected sample. If the result of the supplemental test was discrepant with the initial preliminary positive result, for HIV a western blot was used to rule out a false positive result using Inno-Lia™ HIV I/II Score (Innogenetics, Ghent, Belgium).
Prevalence and incidence rates were calculated for each infection. Prevalence rates were calculated as the number of reactive donations divided by the number of new donors, whereas incidence rates were calculated as the number of seroconverting donors divided by the total number of person-years at risk19,20. Seroconverting donors were donors who, within the study period, initially made a non-reactive donation and thereafter made a reactive donation confirmed to be positive for a transfusion-transmissible infection. The total number of person-years was calculated as described in the relevant literature19,20. HBV adjusted incidence rate were calculated using a method described by Schreiber et al.19.
The residual risk or the probability that a seroconverting donor gave an infected blood unit that went undetected as seropositive during the window period was calculated by multiplying the incidences of seroconversion by the window periods, expressed in fractions of a year. The serological window periods used were 22 days for HIV19,21, 59 days for HBV19,21 and 66 days for HCV22.
Results
During the 3-year study period (2009–2011), 46,018 people were candidates for blood donation, 41,001 donated blood (Table I) and 23,396 made more than one donation.
Table I.
Blood donors screened in the years 2009–2011.
| Years | Blood donation candidates1 | Deferred candidates2 | Selected donors (*)3 | Old donors4 | New donors5 | Family/Replacement donors | Benevolent donors6 | Female | Male |
|---|---|---|---|---|---|---|---|---|---|
| 2009 | 13,123 | 2,113 (16.1%) | 11,010 (83.9%) | 3,440 (31.2%*) | 7,570 (68.8%*) | 6,617 (60.1%*) | 4,393 (39.9%*) | 2,149 (19.5%*) | 8,861 (80.5%*) |
| 2010 | 14,577 | 1,621 (11.1%) | 12,956 (88.9%) | 4,674 (36.1%*) | 8,282 (63.9%*) | 6,177 (47.7%*) | 6,779 (52.3%*) | 2,867 (22.1%*) | 10,089 (77.9%*) |
| 2011 | 18,318 | 1,210 (6.6%) | 17,108 (93.4%) | 7,116 (41.6%*) | 9,992 (58.4%*) | 8,902 (52%*) | 8,206 (48%*) | 4,212 (24.6%*) | 12,896 (75.4%*) |
| 2009–2011 | 46,018 | 4,944 (10.7%) | 41,074 (89.3%) | 15,230 (37.1%*) | 25,844 (62.9%*) | 21,696 (52.8%*) | 19,378 (47.2%*) | 9,228 (22.5%*) | 31,846 (77.5%*) |
All people who presented at the National Blood Centre willing to donate blood;
candidates who were not authorised to give blood because of their medical history or physical examination;
candidates who were cleared for blood donation after blood donor history questionnaires and physical examination;
returning or regular blood donors;
first-time blood donors;
volunteer donors.
% calculated on the basis of selected donors, meaning that the number of selected donors was used as denominator.
Prevalence of viral infections among blood donors
Between 2009 and 2011, the prevalence of HCV among donors increased by a factor of 5, from 1.19% to 6.04%, while the prevalence of HBV decreased from 8.84% to 6.2%. The prevalence of HIV ranged between 2.54% and 3.09% (Table II).
Table II.
Prevalence of infectious-disease markers among first-time donors.
| Reactive donors | All donors | Prevalence rate (%) | |
|---|---|---|---|
| HCV | |||
| 2009 | 90 | 7,570 | 1.19 |
| 2010 | 25 | 8,282 | 0.30 |
| 2011 | 604 | 9,992 | 6.04 |
| 2009–2011 | 719 | 25,844 | 2.78 |
|
| |||
| HBV | |||
| 2009 | 669 | 7,570 | 8.84 |
| 2010 | 165 | 8,282 | 1.99 |
| 2011 | 620 | 9,992 | 6.20 |
| 2009–2011 | 1,454 | 25,844 | 5.63 |
|
| |||
| HIV | |||
| 2009 | 192 | 7,570 | 2.54 |
| 2010 | 299 | 8,282 | 3.61 |
| 2011 | 307 | 9,992 | 3.07 |
| 2009–2011 | 798 | 25,844 | 3.09 |
Incidence of HIV, HCV and HBV seroconversion among blood donors
The incidence rates of HIV (107.3 per 100,000) and HCV (115 per 100,000) seropositivity were similar and were each approximately two times higher than the crude incidence rate of HBsAg (52 per 100,000) (Table III). After adjusting the incidence rate of HBsAg to derive the incidence of HBV (348.4 per 100,000), the HBV infection rate estimate exceeded each of the other rates by a factor of two or more.
Table III.
Seroconversion incidence rates and residual risks of transfusion-transmitted infection in the blood supply associated with window-period donations by converting donors.
| Incidence rates of seroconversion associated with each of three blood-borne pathogens | Residual risks of transfusion-transmitted infection in the blood supply associated with window-period donations by seroconverting donors | ||||
|---|---|---|---|---|---|
|
| |||||
| Infection | N. of seroconversions | N. of person-years | Incidence rate per 100,000 person-years | Length of window period (days) | Estimate of residual risk |
| HIV | 29 | 27,033 | 107.3 | 21 | 1 in 15,462 |
| HBV | 14 | 27,019 | 348.4 (52*) | 59 | 1 in 1,775.7 |
| HCV | 31 | 27,015 | 115 | 66 | 1 in 4,808 |
Incidence rate before correcting to account for the transient antigenemia.
Estimated risk of infectivity among blood donors
Table III shows the estimated probability of viraemia at the time of blood donations that went undetected with the use of current serological tests. We established that the current risk of viral exposure per million donations was 64.7 for HIV, 207.94 for HCV and 534.53 for HBV.
Discussion
Over the period 2009–2011, the risk of HIV transmission was estimated to be 64.7 per 1 million donations (serological screening tests). This risk is very high compared to what is seen in the developed world20,22. The high risk of HIV transmission observed in our setting is explained by our high incidence rate of seroconversion. Thus, the prevention of HIV infection in general population and better selection of donors would be important in reducing the risk of transmitting HIV infection via blood transfusions9.
The prevalences of HIV, HCV and HBV among blood donors were lower than in the general population. Between 2009 and 2011 the prevalence of HCV among blood donors increased by a factor of 5. This increase in HCV prevalence can be explained by a change in the population of donors. Unlike in the preceding years, in 2011, most of the donors were from the HCV high-risk population8 (donors aged between 25 and 64 years old) (data not shown). The risk of HCV transmission between 2009 and 2011 at the Gabonese National Blood Transfusion Centre was estimated to be 207.94 per 1 million donations (serological screening tests). The risk of HBV transmission, which was the highest of the three viruses, was estimated to be 534.53 per 1 million donations. The risk of transfusion-related transmission of HBV has been reported in literature to be higher than that of transmission of HIV and HCV19,20. Overall, the risk of transfusion-transmitted HIV, HCV and HBV infections in the setting of the Gabonese National Blood Transfusion Centre is higher than that in the developed world20, 22–26.
Very few published data exist on the risk of transfusion-transmitted viral infections in sub-Saharan Africa. Lefrère et al.27 reported findings in Blood Transfusion Centres from the Congo, the Ivory Coast, Mali and Senegal, showing lower (1.6–6 times) residual risk for HIV than what we observed at the Gabonese National Blood Transfusion Centre. Jayaraman et al.28 estimated the median overall risks of becoming infected with HIV, HCV and HBV from a blood transfusion in sub-Saharan Africa as 1,000, 2,500 and 4,300 infections per 1 million units, respectively. These estimates are about 15, 12 and 8 times higher than what we observed for HIV, HCV and HBV respectively. Applied to Gabon, the model of Jayaraman et al. estimated HIV, HCV and HBV transfusion transmission risks as 3,030, 5,400 and 9,400 per 1 million units, respectively. These estimates are about 47, 25 and 18 times higher than what we actually observed for HIV, HCV and HBV, respectively. In the absence of real data mathematical models could be useful to quantify transfusion risks, but derived estimates could be lower or even higher than the true risk. In the case of Gabon we found the risks derived from such models were very high compared to the true risk.
Rigorous donor selection and preventive measures such as increasing the coverage of HBV vaccination, adequate disinfection procedures of equipment shared among patients (e.g. in the haemodialysis centre) and all other practices to prevent HIV, HCV and HBV should be taken across sub-Saharan Africa to reduce the risk of transfusion-transmitted viral infections.
Although donor pre-screening and preventive measures to avoid nosocomial infections in the general population have been shown to have a positive impact on the residual risk of transfusion-transmitted infections, the improvement over time of blood screening tests (or diagnostic tools) is an important factor in the reduction of the residual risk of transfusion transmitted infections15,16.
Conclusions
Overall, we believe that stringent donor pre-screening and preventive measures to control infections in the general population must be coupled with new and more sensitive screening tests in order to achieve a significant reduction of the risk of transfusion-transmitted viral infections in Gabon and across sub-Saharan Africa.
Footnotes
Authorship contributions
Leonard Kounegnigan Rerambiah and Joel F. Djoba Siawaya partecipated equally to this work.
The Authors declare no conflicts of interest.
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