Major subjects (18 years and above) voluntary blood donors were the concern of the study. Negative HBsAg and positive anti-HBc antibodies donors were included to this group. They were all contacted by phone to adhere to the study after explanation and invited to come for a consultation at the Hepato-gastroenterology unit of Yalgado Ouédraogo teaching hospital. Those who didn’t come for consultation and those who were not in accordance with the study were excluded.

Pre-donation medical interview

Medical interview was the first obligatory step. It involves both qualified health personnel and donor candidate. It is a questionnaire to which candidates for blood donation are submitted. This interview consisted in finding eventual risk factors for the donor and for the recipient by identifying different pathologies transmissible or not which can develop in the donor and/or the recipient.

Blood collection

At the end of the medical interview, the candidate deemed fit for donation is taken to an appropriate room where blood is collected in individual bags identified by numbers, containing anticoagulant and conservative solution. Simultaneously, two biologic samples were collected in tubes. Different test were carried out on these samples for biologic qualification of the donation.

Sample laboratory analysis

The following tests were carried out on biologic samples contained in the tube: blood group (ABO and Rhesus); the investigation of HBsAg, human immunodeficiency virus (HIV) antibodies, syphilis antibodies and hepatitis C virus (HCV) antibodies. These tests were carried out free of charge by NCBT laboratory.

Results delivery

Results of the tests carried out were available in about three weeks after the donation, and each donor was invited to come and collect his/her result at the Center of blood transfusion every afternoon of opened days.

First phase of collection

At the end of the first donation analysis, all negative HBsAg serums were selected for investigation of anti-HBc antibodies. The negative HBsAg serums and positive anti- HBc antibodies were retained for the study.

Specialized consultation

The negative HBsAg donors with positive anti-HBc antibodies were consulted at the Hepato-gastroenterology unit of Yalgado Ouédraogo teaching hospital. The consultation comprises three steps:

A questionning on viral hepatitis particularly on hepatitis B concerning epidemiology, types of viruses, mode of contamination, evolution of HBV, treatment and means of prevention.

After a physical examination, a biologic assessment, comprising the viral load of HBV and the dosage of anti-HBs antibodies, were requested.

A questionnaire was administered at the end.

The second phase of data collection

It deals with donors who were received in external consultation and who gave their concerns. The viral load and titration of anti-HBs antibodies were requested after consultation. The cost of these additional tests was at the patient’s charge.

The immunoenzymatic tests were used to detect HBsAg: Determine^TM (Abbott) and Elisa (Vidas^®) thanks to fourth (4^th) generation reagents used on robot. The tests were used according to the manufacturer’s instructions.

Rapid tests were used for anti-HBs antibodies: One Step HBc Ab (Serum/plasma). It is an immunochromatographic test which principle is the immunologic dosage in sandwich for the detection of anti-HBc antibodies in serum/plasma.

HBV DNA quantification was carried out using real time PCR in one of the four qualified laboratories of Ouagadougou chosen by patients, (CERBA, CHUYO, CMA Schiphra and “laboratoire d’analyses médicales du centre”). The detection points varied according to the type device used.

The DNA was considered as detectable if its level was superior to the manufacturer’s detection threshold point (Table 1). Different Labs show a detection level higher than 10 IU/ml for ant-HBs antibodies, protective against HBV. Once the viral load was detectable, a complementary assessment was requested. It has consisted of a complete hepatic assessment (transaminase biologic tests, total bilirubin, alkaline phosphatases, gamma-glutamyl transpeptidase, alpha foeto-protein, full blood count, the Fibrometer® …), other HBV markers (HBeAg and anti-HBe antibodies), and morphologic ex-

aminations (abdominal ultrasound, abdominal CT scan, gastroscopy) related to the clinical context.

The patients were introduced in the HBV classical care system at the gastro- enterology unit. The data collected were analysed using microcomputer with the aid of software like Epi info 3.5.4 (French version). The analysis of data collected used Epi info software (3.5.4 French version) on microcomputer.

A total of 1980 serums from negative HBsAg donors were tested for anti-HBs antibodies, among which 872 (44%) were positives. These 872 were called for specialized consultation and 160 responded. Among the 160 donors, 76 were able to realise DNA quantification which was detectable in 25 (32.8%).

The 32.8% OBI prevalence is shown (25 of the 76 who undertook the HBV DNA quantification). There were 20 men and 5 women given a sex ratio of 4. The age range was 24 to 54 years old with a mean age of 33.15 years. The age class 21 to 30 was the most represented with 15 cases.

Surgical and medical histories in favour of HBV transmission were found in donors (Table 2).

The physical examination was normal in 25 donors.

The mean viral load was 954 IU/ml (5550 copies). A donor has a viral charge of 73672 IU/ml (greater than 2000 IU/ml).

Thirteen on twenty-five (52%) had an anti-HBs level higher than 10 IU/ml (positive) and the twelve others had less than 10 IU/ml (negative).

HBeAg was negative in all the 25 while anti-HBe antibodies were positive in 18 cases.

Among the 25 donors, there was one HIV co-infection case and none of HCV infection.

Hepatobiliary ultrasound done by 20 patients was normal. The biologic assessment highlights a moderate cytolysis of 2 times the normal upper limit at the expense of AST in the positive HIV patient. Alpha-fetoprotein and hepatic fibrosis were not assessed.

Our study has some limitations. Despite our explanations in the phone to convince them, many anti-HBc positive donors did not see the need to come and visit. Among 872 donors called only 160 had responded. For them they are not seek and do not understand the need to spend their money in transport and additional tests. Otherwise the fact that the cost of the tests was in patient’s charge (Vial load around $100 US, anti-HBs $15US...) has been a strong bias of selection. Because only the donors able to pay their tests were included. Among 160 donors who responded only 76 were able to realize their tests and were really included in this study. We agree that there is probably a bias in this study.

Occult hepatitis B infection prevalence is highly variable (Table 3), since figures in the literature are ranged from 0 to 50% [1] . In our study, among 76 tested samples, 25 were found detectable thus an occult hepatitis B infection prevalence of 32.8% in blood donors. Our result is higher than those of Coulibaly M L [2] , Moresco M. Ndos S [3] , Said ZN [4] and Oluyinka OO [5] in 2015 whose prevalence were respectively:

- 6.12% in a series of 147 haemodialysed patients;

- 2.7% samples were negative for HBsAg and positive for HBV DNA in 3600;

- 17% occult hepatitis B infection in blood donors;

- 17.2% occult hepatitis B infection in 3167 negative HBsAg donors.

Prevalence lower than that of our study: 0.006%, 0.22%, 0.05% and 0.0006% were reported by Oluyinka OO et al. [5] in Poland, Italy, Spain and Germany respectively; they are low endemic countries.

The high prevalence of occult hepatitis B infection in our study can be attributable to the fact that Burkina Faso belongs to a high HBV endemic area, the small tested sample size for DNA and also the improvement in more sensitive DNA detection technics (real time PCR). This poses a real problem of transfusion security in our countries. HBsAg was the only sought marker to distinguish donors, it is true that blood bags containing viral DNA are transfused everyday here in Burkina Faso to recipients who are mostly children suffering from severe anaemia particularly due to malaria.

In our study, we have noted an anti-HBc antibodies portage prevalence of 44% (872/1980) in negative HBsAg donors. Barro L [11] , also found a portage prevalence of 38.07% in negative HBsAg donors in 2014 in Burkina, while in 2015 in Cameroon, Biwole reported a higher anti-HBc antibodies portage prevalence of 57% in a similar population.

The presence of anti-HBc antibodies shows that there was a contact with the HBV, be it a chronic hepatitis B (positive HBsAg for more than 6 months with positive anti-HBc antibodies) or occult hepatitis B infection (negative HBsAg with detectable DNA) or a cured hepatitis B (negative HBsAg, undetectable DNA and positive anti-HBc antibodies). Any positive anti-HBc antibodies patient is prone to a reactivation of hepatitis B in case of immunodepression, be it iatrogenic (chemotherapy, organ transplantation) or acquired (HIV infection).

The age range was 24 to 54 years old with a mean age was 33.15 years. The sex ratio was

HB: hepatitis B; OBI: occult hepatitis B infection; PCR: “polymerase chain reaction”; RT: “real time”; HCV: “hepatitis C virus”; HIV: “human immunodeficiency virus”.

4. The male predominance is due to the fact that females generally participate poorly to blood donation and also to the high cost of complementary exams. The fact that tests cost was borne by patient constituted a real selection bias.

Surgical and medical histories in favour of HBV transmission were found in donors. Collective use of sharp objects was noted. Nails clipper (8 donors), razor (4 donors), blade (3 donors) and some harmful traditional practices such as female genital mutilation which had been performed in 3 women of our study.

These practices in our regions contribute to promote and maintain the transmission of HBV and other diseases transmissible via biologic fluids.

Hepathopatic signs were not noted in our study. However, the following clinical situations could be some circumstances of occult hepatitis B discovery

Transmission of occult hepatitis B viral infection to a recipient

During assessment of hepatitis; it is generally acute in a recipient. Post-transfusion risk in France is 1/450000 (2 times higher to that of hepatitis C and 4 times higher to that of HIV). This HBV transmission risk to positives anti-HBs antibodies subjects was demonstrated [6] .

Reactivation of an occult hepatitis B viral infection is described in literature during an immunosuppression in case of chemotherapy, graft (kidney, bone marrow, liver) and immune deficiencies [18] . Vallet-Pichard A and Pol S, in 2008 found a viral reactivation frequency of 0.5% in renal transplantation and of 5% in hematopoietic stem cells graft in recipients with positive anti-HBc antibodies [1] .

Chronic diseases of the liver and occult hepatitis B viral infection

We did not evaluate fibrosis in our study; however, no evocative sign of chronic hepatopathy was noted during clinical examination and ultrasound.

Occult hepatitis B viral infection in hemodialysed patients

Many studies confirm a relatively high frequency of occult hepatitis B viral infection in hemodialysed patients [2] [19]

Hepatocellular carcinoma (HCC) [20]

No case of HCC was noted in our study on condition of the anatomo-pathologic test which was not carried out in our patients. The occult hepatitis B viral infection prevalence varies from 10% - 60% and even more in case of HCC with unknown aetiology [1] .

Occult hepatitis B is a complex biologic entity.

Viral charge (viral DNA)

About two third (50/76) of viral charges were carried out using PCR/Applied biosystems 7500 platform technic. The detection point with this technic was the lowest (lower detection limit is at 02 copies/ml) of the four used technics (Table 1). For 25 cases of detectable DNA in this study, the HBV viral charges were ranged between 2.23 and 3672.68 IU/ml with a mean value of 954 IU/ml corresponding to 13-428775 copies/ml with a mean value of 5550 copies/ml. Only one donor had a viral charge greater than 2000 IU/ml (73,672 IU/ml). In Nigeria, Oluyinka O [5] reported a viral charge comprised between 18.4 and 224.3 IU/ml and one of his patients had a viral charge greater than 4000 IU. Candotti et al. [21] noted a viral charge between undetectable and 5640 IU/ml with a median of 25 IU/ml in Europe. Viral charge is generally low in literature in case of occult hepatitis B (less than 4 logs) [1] [22] . Sequencing of HBV was not carried out in our series, but Allain J P et al. [23] found predominance of genotype A and genotype D.

Anti-HBs antibody

In our study, thirteen donors on twenty-five (52%) had an anti-HBs antibodies level greater than 10 IU/ml. Raimondo G. [24] found among his anti-HBs antibodies carriers that 75% had protective concentration (>10 IU/ml) while Oluyinka O et al. [5] reported a protective anti-HBs antibodies percentage of 30%.

Anti-HBc antibody

We noted an anti-HBc antibodies portage prevalence of 44% (872/1980). This high portage prevalence of anti-HBc antibodies were seen in many series mostly in high endemic countries [20] [25] [26] . Oluyinka O [5] reported a portage prevalence of 43.05% in donors in Nigeria while that of Said Z N [10] in Egypt was lower, 14.2%. We think that anti-HBc antibodies portage is the enlarged reflection of the prevalence of hepatitis B in a given area. OBI prevalence is high in subjects with positive anti-HBc antibodies especially in the absence of anti-HBs antibodies.

Other complementary tests

A case of HIV/HBV co-infection with a viral charge HBV at 420 copies was noted. The standard biologic assessment of the liver (transaminases, bilirubin, gamma glutamyl transpeptidase, alkaline phosphatases, prothrombin levels…) was normal even hepato-biliary ultrasound. Occult hepatitis B is a chronic hepatitis usually inactive.