Clinical algorithms for the screening of pregnant women for STDs in Libreville, Gabon: which alternatives?

OBJECTIVE: Sexually transmitted diseases (STDs) remain one of the major public health problems in the developing world. To implement a systematic screening of STDs among pregnant women in Libreville, Gabon, a preliminary cross sectional study on STD prevalence and risk factors was performed in antenatal clinics. A score, integrating risk factors and elementary clinical signs for the screening of STDs, showed higher performances compared with hierarchical algorithms. The prospective validation of this score based on six criteria (risk factors and simple clinical signs) was done in 1994-5. The sensitivity (76.7%), compared with results from other studies, was acceptable for diagnosing cervical infection (Neisseria gonorrhoeae and/or Chlamydia trachomatis) but the specificity was low (50.6%). In addition, the diagnostic values for diagnosing vaginal infection (Trichomonas vaginalis and/or Candida albicans) were poor. We then proposed to evaluate an alternative flowchart for the screening of cervical and vaginal infections. METHODS: In this study, 646 pregnant women were enrolled. Each woman was interviewed and examined by a physician and then was subjected to reference laboratory examinations. An algorithm in two steps, combining a risk assessment score at the beginning of a hierarchical process, followed by a second step more specifically applied to a limited number of women, was developed and evaluated. RESULTS: The prevalence rate was 11.3% for cervical infection and 39.5% for vaginal infection. The first step of the algorithm, applied to all pregnant women, is based on four criteria (age, marital status, dyspareunia, coloured vaginal discharge). It allows classification of the women into three classes: high, low, and intermediate risk of cervical infection. Only the patients with intermediate risk were submitted to further investigations including speculum and microscopic examination, and subsequently chlamydial antigen detection. This flowchart was 83.6% and 81.2% sensitive and 63.4% and 62.7% specific for predicting cervical infection and vaginal infection, respectively. CONCLUSION: Similar strategies using simple rapid tests for chlamydial and gonococcal infection would certainly constitute a good diagnostic tool. This theoretical model needs to be evaluated prospectively, not only to confirm their diagnostic value but also to evaluate their feasibility, reliability and acceptability, as well as their cost effectiveness.

Prospective evaluation of a flow chart using a risk assessment for the diagnosis of STDs in primary healthcare centres in Libreville, Gabon.

BACKGROUND: The serious impact of STDs on women and children in particular, and the linkage between STDs and HIV infection are a profound concern to public health worldwide. One of the main strategies against STDs is based on early diagnosis and treatment. However, this approach is limited by the lack of appropriate laboratory facilities. A syndromic approach has been recommended by the WHO but needs to be evaluated under field conditions. A preliminary cross sectional study on STD prevalence and risk factors in Libreville showed that 13.5% of pregnant women had gonococcal and/or chlamydial infection which justifies systematic screening of STDs. Based on the results of this study, different flow charts with or without a risk factor assessment (score) were designed. The flow chart with the best performances for diagnosing chlamydial or gonococcal cervical infection and routinely acceptable, was a score algorithm, based on two risk factors (age and marital status) and four simple clinical signs (pelvic or lumbar pain, vaginal discharge and its characteristics). Sensitivity and specificity were 76.9% and 40.4% respectively. Thus, the objective of this study was to evaluate this strategy under field conditions. METHODS: A prospective study among pregnant women attending antenatal clinics was done. The score was applied to each woman by a midwife and a physician, and specimens were collected for the reference laboratory tests. Validation of the algorithm was done by comparing the performances with the gold standard laboratory diagnosis. RESULTS: 646 pregnant women were enrolled. The prevalence of cervical infection was 11.3. The sensitivity and specificity of this algorithm recorded by the midwives were 73.3% and 54.8%, respectively and by the physician 76.7% and 50.6%. The proportion of women correctly classified by the midwives and by the physician was not significantly different. CONCLUSION: The score applied was well accepted by healthcare workers and patients, and was routinely practised. Results obtained by the midwives and by the physician were similar. Thus, the use of flow charts which adds a risk assessment to the syndromic approach for diagnosing cervical infections is feasible. However, the performances of such flow charts need to be improved before being used routinely.

Geographical distribution of HIV-1 group O viruses in Africa.

OBJECTIVE: To determine to what extent HIV-1 group O strains are present in different African countries. MATERIALS AND METHODS: A total of 14,682 samples of sera from a range of patients from 12 different African countries were tested. All the sera were tested with an enzyme-linked immunosorbent assay (ELISA) using a combination of V3 peptides from ANT-70 and MVP-5180. Samples reactive in ELISA were retested in a line immunoassay (LIA-O). Samples reactive in ELISA were also retested with an in-house Western blot to determine the presence of antibodies to gp120 of HIV-1 ANT-70. Polymerase chain reaction was performed on HIV-1 group O and group O indeterminate sera. RESULTS: Of all the sera samples tested, only 19 sera had antibodies to group O V3 peptides exclusively and 46 were indeterminate for group O infection in LIA-O. The highest prevalence of HIV-1 group O infection among HIV-positive sera was observed in Cameroon (2.1%) and neighbouring countries, 1.1% in Nigeria and 0.9% in Gabon. The lowest rates were seen in west Africa: 0.07% in Senegal, 0.14% in Togo, 0.16% in Chad and 0.3% in Niger. Group O sera were observed in almost all the population categories tested. The ANT-70 V3 peptide in LIA-O was reactive with all of the sera considered to be HIV-1 group O antibody positive by LIA, versus 78.9% for the MVP-5180 peptide. Thirteen out of 19 group O samples of sera were tested in PCR. Eight samples were identified as group O by specific group O pol and/or V3 primers; in the remaining five samples no HIV RNA could be detected. Of the indeterminate sera samples, two were identified as group O. CONCLUSION: In eight of the 12 countries tested, antibodies to group O viruses were identified. Numbers of HIV-1 group O viruses are low. Their presence is not restricted to Cameroon and neighbouring countries but can also be found in west and south-east Africa.

PIP: An enzyme-linked immunosorbent assay (ELISA), using a combination of V3 peptides and ANT-70 and MVP-5180, was used to test 14,682 sera samples from people living in Burkina Faso, Burundi, Cameroon, Chad, Congo, Gabon, Mali, Niger, Nigeria, Senegal, Togo, and Zambia to examine the geographic spread of HIV-1 group O viruses in Africa. An in-house Western blot and a line immunoassay (LIA-O) were used to detect the presence of antibodies to gp120 of HIV-1 ANT-70 of samples reactive in ELISA and then a polymerase chain reaction (PCR) on HIV-1 group O and group O indeterminant sera. HIV-1 group O antibodies were present in 8 countries (Cameroon, Chad, Gabon, Niger, Nigeria, Senegal, Togo, and Zambia). Among these 8 countries, the prevalence of HIV-1 group O sera ranged from 2.1% in Cameroon to 0.07% in Senegal. Cameroon and its neighboring countries had a higher prevalence than the West African countries (0.9-2.1% vs. 0.07-0.3%) and Zambia. HIV-1 group O virus was more or less evenly distributed among the population groups tested. The ANT-70 V3 peptide in LIA-O had a higher reactivity rate with HIV-1 group O sera than MVP-5180 V3 peptide in LIA-O (100% vs. 78.9%). 8 of the 13 samples tested in PCR were identified as group O by specific group O pol and/or V3 primers. Among the remaining 5 indeterminant sera samples, 2 were identified as group O. Prospective studies are needed to monitor the true prevalence of HIV-1 group O viruses in Cameroon, its neighboring countries, and West Africa. They are also needed to determine the risk factors associated with group O infection. Monitoring these viruses will allow adaptation of HIV testing strategies for blood screening and serodiagnosis if required.

Epidemiological and molecular characteristics of HIV infection in Gabon, 1986-1994.

OBJECTIVE: To describe trends in the prevalence of HIV-1 infection in different populations in Gabon, and the molecular characteristics of circulating HIV strains. METHODS: Data were collected on HIV prevalence through sentinel surveillance surveys in different populations in Libreville (the capital) and in Franceville. In Libreville, a total of 7082 individuals (hospitalized patients, tuberculosis patients, pregnant women, asymptomatic adults, prisoners) were recruited between 1986 and 1994. In Franceville, we tested 771 pregnant women and 886 healthy asymptomatic adults (1986-1988). Sera were screened for HIV antibodies by enzyme-linked immunosorbent assay (ELISA) and confirmed by Western blot or line immunoassay (LIA). Reactive samples in ELISA were tested for the presence of antibodies to HIV-1 group O viruses by ELISA using V3 peptides from HIV-1 ANT-70 and HIV-1 MVP-5180 followed by confirmation by LIA and a specific Western blot. Seventeen HIV-1 strains were isolated (1988-1993) and a 900 base-pair fragment encoding the env region containing V3, V4, V5 and beginning of gp41 was sequenced and a phylogenetic tree was constructed. RESULTS: HIV prevalence was relatively low and remained stable (0.7-1.6% in pregnant women, 2.1-2.2% in the general population). The prevalence was also stable among prisoners (2.1-2.6%). Among hospitalized and tuberculosis patients prevalence was higher and increased (1.8-12.7% and 1.5-16.2%, respectively). Only three sera had antibodies to HIV-1 group O. The 17 HIV-1 strains represent six different genetic subtypes including type O. CONCLUSION: Our data from 1986 to 1994 show a stable and low HIV prevalence in Gabon, and a high genetic diversity of HIV-1 strains. This, also observed in Cameroon, is in contrast to that found elsewhere in Africa. Differences in rate of spread of HIV infection are probably explained by interplay between numerous factors. The role of different HIV subtypes in the dynamics of the HIV epidemic should be examined further.

[Development and evaluation of screening algorithms for sexually transmitted diseases in pregnant women at Libreville, Gabon]. / Elaboration et évaluation d'algorithmes de dépistage des MST chez la femme enceinte à Libreville, Gabon.

The struggle against sexually transmitted diseases (STD) constitutes a priority of public health in developing countries: STD cause complications, particularly in pregnant women, and facilitate the transmission of HIV. One of the strategies in the struggle against STD is the diagnosis and the early treatment of these infections. The STD, and in particular infections of Neisseria gonorrhea and Chlamydia trachomatis, are difficult to diagnose in women without complementary analyses, which primary health care may not be able to supply. Health care provided to patients could be standardized and improved by considering the signs and symptoms. We studied the prevalence and risk factors of STD among 192 pregnant women consulting the health clinic in Libreville, Gabon, in September 1993. The prevalence of STD was high (13.5% rate of cervical infection with gonorrhea or Chlamydia trachomatis). We then evaluated the different diagnostic strategies or algorithms. Regardless of the type of examination (medical interview, simple clinical examination or examination with a speculum), the use of scores integrating risk factors, the clinical signs and symptoms outperformed hierarchical algorithms. This approach was more sensitive and specific and easy to perform. Use of this method may enable more effective screening of STD and also avoid most maternal and perinatal complications.