Sana Sambou

Effect of the introduction of pneumococcal conjugate vaccination on invasive pneumococcal disease in The Gambia: a population-based surveillance study

Summary Background Little information is available about the effect of pneumococcal conjugate vaccines (PCVs) in low-income countries. We measured the effect of these vaccines on invasive pneumococcal disease in The Gambia where the 7-valent vaccine (PCV7) was introduced in August, 2009, followed by the 13-valent vaccine (PCV13) in May, 2011. Methods We conducted population-based surveillance for invasive pneumococcal disease in individuals aged 2 months and older who were residents of the Basse Health and Demographic Surveillance System (BHDSS) in the Upper River Region, The Gambia, using standardised criteria to identify and investigate patients. Surveillance was done between May, 2008, and December, 2014. We compared the incidence of invasive pneumococcal disease between baseline (May 12, 2008–May 11, 2010) and after the introduction of PCV13 (Jan 1, 2013–Dec 31, 2014), adjusting for changes in case ascertainment over time. Findings We investigated 14 650 patients, in whom we identified 320 cases of invasive pneumococcal disease. Compared with baseline, after the introduction of the PCV programme, the incidence of invasive pneumococcal disease decreased by 55% (95% CI 30–71) in the 2–23 months age group, from 253 to 113 per 100 000 population. This decrease was due to an 82% (95% CI 64–91) reduction in serotypes covered by the PCV13 vaccine. In the 2–4 years age group, the incidence of invasive pneumococcal disease decreased by 56% (95% CI 25–75), from 113 to 49 cases per 100 000, with a 68% (95% CI 39–83) reduction in PCV13 serotypes. The incidence of non-PCV13 serotypes in children aged 2–59 months increased by 47% (−21 to 275) from 28 to 41 per 100 000, with a broad range of serotypes. The incidence of non-pneumococcal bacteraemia varied little over time. Interpretation The Gambian PCV programme reduced the incidence of invasive pneumococcal disease in children aged 2–59 months by around 55%. Further surveillance is needed to ascertain the maximum effect of the vaccine in the 2–4 years and older age groups, and to monitor serotype replacement. Low-income and middle-income countries that introduce PCV13 can expect substantial reductions in invasive pneumococcal disease. Funding GAVIs Pneumococcal vaccines Accelerated Development and Introduction Plan (PneumoADIP), Bill & Melinda Gates Foundation, and the UK Medical Research Council.

Elimination of Lymphatic Filariasis in The Gambia

Background The prevalence of Wuchereria bancrofti, which causes lymphatic filariasis (LF) in The Gambia was among the highest in Africa in the 1950s. However, surveys conducted in 1975 and 1976 revealed a dramatic decline in LF endemicity in the absence of mass drug administration (MDA). The decline in prevalence was partly attributed to a significant reduction in mosquito density through the widespread use of insecticidal nets. Based on findings elsewhere that vector control alone can interrupt LF, we asked the question in 2013 whether the rapid scale up in the use of insecticidal nets in The Gambia had interrupted LF transmission. Methodology/Principal Finding We present here the results of three independently designed filariasis surveys conducted over a period of 17 years (1997–2013), and involving over 6000 subjects in 21 districts across all administrative divisions in The Gambia. An immunochromatographic (ICT) test was used to detect W. bancrofti antigen during all three surveys. In 2001, tests performed on stored samples collected between 1997 and 2000, in three divisions, failed to show positive individuals from two divisions that were previously highly endemic for LF, suggesting a decline towards extinction in some areas. Results of the second survey conducted in 2003 showed that LF was no longer endemic in 16 of 21 districts surveyed. The 2013 survey used a WHO recommended LF transmission verification tool involving 3180 6–7 year-olds attending 60 schools across the country. We demonstrated that transmission of W. bancrofti has been interrupted in all 21 districts. Conclusions We conclude that LF transmission may have been interrupted in The Gambia through the extensive use of insecticidal nets for malaria control for decades. The growing evidence for the impact of malaria vector control activities on parasite transmission has been endorsed by WHO through a position statement in 2011 on integrated vector management to control malaria and LF.

Monitoring the introduction of pneumococcal conjugate vaccines into West Africa: design and implementation of a population-based surveillance system.

Philip Campbell Hill and colleagues describe how they set up a population-based surveillance system to assess the impact of pneumococcal conjugate vaccines on invasive pneumococcal disease (IPD) and radiological pneumonia in children in The Gambia.

The Effectiveness of Conjugate Haemophilus influenzae Type B Vaccine in The Gambia 14 Years After Introduction

Fourteen years after the first introduction of conjugate Haemophilus influenzae type b vaccine in The Gambia, effective disease control was maintained, with associated low carriage and high seroprotection. Continued surveillance must determine if protection wanes and a booster dose is needed.

Incidence of Haemophilus influenzae Type b Disease in The Gambia 14 Years after Introduction of Routine Haemophilus influenzae Type b Conjugate Vaccine Immunization

OBJECTIVE Haemophilus influenzae type b (Hib) conjugate vaccine was first introduced in Africa in The Gambia in 1997 as a primary 3-dose course in infancy with no booster, and was followed by the disappearance of invasive Hib disease by 2002. A cluster of cases detected non-systematically in post-infant children in 2005-2006 raised the question of the need for a booster dose. The objective of this study was to determine the incidence of invasive Hib disease in Gambian children 14 years after the introduction of Hib conjugate vaccine. STUDY DESIGN This hospital-based clinical and microbiological Hib disease surveillance in 3 hospitals in the western region of The Gambia was undertaken between October 2007 and December 2010 applying the same methods used in a previous Hib vaccine effectiveness study in 1997-2002. RESULTS The annual incidences of Hib meningitis and all invasive Hib disease in children aged <5 years remained below 5 cases per 100,000 children during 2008-2010. The median age of patients with any invasive Hib disease was 5 months. CONCLUSION Hib conjugate vaccination as a primary 3-dose course in The Gambia remains highly effective in controlling invasive Hib disease, and current data do not support the introduction of a booster dose.

Increased Disease due to Haemophilus influenzae Type b Population-based Surveillance in Eastern Gambia, 2008-2013

Background: In 1997, The Gambia became the first African country to introduce conjugate Haemophilus influenzae type b (Hib) vaccine with good disease control through to 2010. Methods: Culture-based surveillance for invasive bacterial disease in eastern Gambia, specifically the Basse Health and Demographic Surveillance System (BHDSS) area, was conducted from 12 May 2008 and in Fuladu West district from 12 September 2011 until 31 December 2013. In 2011, Hib serology was measured in 5–34-year-olds. Results: In all, 16,735 of 17,932 (93%) eligible patients were investigated. We detected 57 cases of invasive H. influenzae disease; 24 (42%) were type b. No cases of Hib disease were detected in the BHDSS area in 2008–2009; 1 was detected in 2010, 2 in 2011, 4 in 2012 and 7 in 2013. In 2013, the incidence of Hib disease in those aged 2–11 and 2–59 months in the BHDSS area was 88 [95% confidence interval (CI): 29–207] and 22 (95% CI: 9–45) cases per 105 person-years, respectively. In 2013, disease incidence in Fuladu West among those aged 0–59 months was 26 (95% CI: 7–67) cases per 105 person-years. Nine of 24 Hib cases were vaccine failures (2 HIV positive) and 9 were too young to have been vaccinated. The proportion of children aged 5–6 years (n = 223) with anti-Hib IgG ≥1.0 &mgr;g/mL was 67%; the antibody nadir was in 9–14-year-olds (n = 58) with 55% above threshold. Conclusions: Hib disease in eastern Gambia has increased in recent years. Surveillance in developing countries should remain alert to detect such changes.

Impact of the introduction of pneumococcal conjugate vaccination on pneumonia in The Gambia: population-based surveillance and case-control studies

Summary Background Pneumococcal conjugate vaccines (PCVs) are used in many low-income countries but their impact on the incidence of pneumonia is unclear. The Gambia introduced PCV7 in August, 2009, and PCV13 in May, 2011. We aimed to measure the impact of the introduction of these vaccines on pneumonia incidence. Methods We did population-based surveillance and case-control studies. The primary endpoint was WHO-defined radiological pneumonia with pulmonary consolidation. Population-based surveillance was for suspected pneumonia in children aged 2–59 months (minimum age 3 months in the case-control study) between May 12, 2008, and Dec 31, 2015. Surveillance for the impact study was limited to the Basse Health and Demographic Surveillance System (BHDSS), whereas surveillance for the case-control study included both the BHDSS and Fuladu West Health and Demographic Surveillance System. Nurses screened all outpatients and inpatients at all health facilities in the surveillance area using standardised criteria for referral to clinicians in Basse and Bansang. These clinicians recorded clinical findings and applied standardised criteria to identify patients with suspected pneumonia. We compared the incidence of pneumonia during the baseline period (May 12, 2008, to May 11, 2010) and the PCV13 period (Jan 1, 2014, to Dec 31, 2015). We also investigated the effectiveness of PCV13 using case-control methods between Sept 12, 2011, and Sept 31, 2014. Controls were aged 90 days or older, and were eligible to have received at least one dose of PCV13; cases had the same eligibility criteria with the addition of having WHO-defined radiological pneumonia. Findings We investigated 18 833 children with clinical pneumonia and identified 2156 cases of radiological pneumonia. Among children aged 2–11 months, the incidence of radiological pneumonia fell from 21·0 cases per 1000 person-years in the baseline period to 16·2 cases per 1000 person-years (23% decline, 95% CI 7–36) in 2014–15. In the 12–23 month age group, radiological pneumonia decreased from 15·3 to 10·9 cases per 1000 person-years (29% decline, 12–42). In children aged 2–4 years, incidence fell from 5·2 to 4·1 cases per 1000 person-years (22% decline, 1–39). Incidence of all clinical pneumonia increased by 4% (–1 to 8), but hospitalised cases declined by 8% (3–13). Pneumococcal pneumonia declined from 2·9 to 1·2 cases per 1000 person-years (58% decline, 22–77) in children aged 2–11 months and from 2·6 to 0·7 cases per 1000 person-years (75% decline, 47–88) in children aged 12–23 months. Hypoxic pneumonia fell from 13·1 to 5·7 cases per 1000 person-years (57% decline, 42–67) in children aged 2–11 months and from 6·8 to 1·9 cases per 1000 person-years (72% decline, 58–82) in children aged 12–23 months. In the case-control study, the best estimate of the effectiveness of three doses of PCV13 against radiological pneumonia was an adjusted odds ratio of 0·57 (0·30–1·08) in children aged 3–11 months and vaccine effectiveness increased with greater numbers of doses (p=0·026). The analysis in children aged 12 months and older was underpowered because there were few unvaccinated cases and controls. Interpretation The introduction of PCV in The Gambia was associated with a moderate impact on the incidence of radiological pneumonia, a small reduction in cases of hospitalised pneumonia, and substantial reductions of pneumococcal and hypoxic pneumonia in young children. Low-income countries that introduce PCV13 with reasonable coverage can expect modest reductions in hospitalised cases of pneumonia and a marked impact on the incidence of severe childhood pneumonia. Funding GAVIs Pneumococcal vaccines Accelerated Development and Introduction Plan, Bill & Melinda Gates Foundation, and UK Medical Research Council.

Field evaluation of a schistosome circulating cathodic antigen rapid test kit at point-of-care for mapping of schistosomiasis endemic districts in The Gambia

Background Studies in Sub Saharan Africa have shown that the Circulating Cathodic Antigen point-of-care-test (POC-CCA) is more accurate in the detections of S. mansoni than the microscopic Kato-Katz technique but less is known about the accuracy of this rapid test in detecting S. haematobium infections. This study was intended to evaluate the field accuracy of POC-CCA as a rapid test kit for schistosomiasis mapping in The Gambia. Methods This prospective study was conducted in 4 regions in the country. Ten schools were randomly selected from each region, and a total of 2018 participants whose ages range from 7 to 14 years were enrolled in the study. Stool and urine samples were collected from each participant from May to June 2015, and tested for S. haematobium and S. mansoni infections in field and laboratory settings. The tests conducted included POC-CCA, double Kato-Katz slides, urine filtration and dipstick for hematuria. Results Of the 1954 participants that had complete data, the mean age of participants was 9.9 years. The prevalence of children infected with S. haematobium, using urine filtration technique was 10.1% (95% CI: 8.87–11.55). Central River Region had the highest level of urinary schistosomiasis with a prevalence of 28.0% (24.13–32.12).The lowest urinary schistosomiasis prevalence of 0.6% (0.12–1.86) was found in Lower River Region and North Bank Region had no cases of schistosomiasis detected. Only 5 participants were infected with S. mansoni. Using urine filtration as reference standard for the detection of S. haematobium, the sensitivity and specificity of POC-CCA was 47.7% and 75.8%. Whilst sensitivity and specificity of POC-CCA for detecting S. mansoni were 60.0% and 71.2% using double Kato-Katz as reference standard. Conclusion This study showed lower sensitivity of POC-CCA in detecting S. haematobium. Therefore POC-CCA is less useful for rapid diagnosis of urinary schistosomiasis.

Prevalence and risk factors for faecal carriage of Extended Spectrum β-lactamase producing Enterobacteriaceae among food handlers in lower basic schools in West Coast Region of The Gambia

Background The isolation of Extended spectrum βlactamase (ESBLs) producing Enterobacteriaceae among food handlers and their implication as sources of food borne outbreaks are a public health concern. This study seeks to investigate the prevalence of faecal carriage of these bacteria among food handlers in the West Coast Region of The Gambia. Method This study enrolled 600 participants from 60 Lower Basic Schools in West Coast Region of the country. Stool samples collected from the participants were presumptively screened for the ESBLs producing Enterobacteriaceae, using Drigalski agar, supplemented with 2mg/L cefotaxime. The bacterial colonies that grew on each Drigalski agar were tested for ESBL production by the double disk synergy test as recommended by Clinical and Laboratory Standard Institute (CLSI-2015). The confirmatory analysis for ESBL was determined as the zone of inhibition of cefotaxime and/or ceftazidime to ≥5mm from that of cefotaxime /clavulanicacid and/or ceftazidime/clavulanic acid. The presumptive screening of isolates for AmpC phenotypes was done by testing the organism against cefoxitin. The prevalence of the ESBL carriage was presented in percentages. The association of risk factors to the faecal carriage of ESBLs producing Enterobacteriaceae was performed by Pearson Chi-squared and Fishers Exact at (p ≤ 0.05). Result The prevalence of faecal carriage ESBL producing Enterobacteriaceae among food handlers was 5.0% (28/565). We found50% (14/28) and3.57% (1/28) ESBL producing bacteria were presumptive AmpC and carbapenemase resistance phenotype. Themost abundant ESBL producing Enterobacteriaceae were Klebsiella spp 32.1% (9/28) and Escherichia spp 28.6% (8/28). The use of antibiotics in the last 3 months was found to be significantly associated (P = 0.012) with the faecal carriage of ESBLs producing Enterobacteriaceae. Conclusion The prevalence of faecal carriage of ESBLs producing Enterobacteriaceae among food handlers in the Gambia is low. The history to use of the antibiotics in the last three months was found to be significantly associated with this prevalence. Therefore, the institution of a robust antimicrobial surveillance and treatment of patients with such infections are necessary to curb the spread of these multidrug resistant bacteria in the country. Rational prescription and usage of the antibiotics especially cephalosporin should be advocated both in public and private health facilities.

Use of Antibody Tools to Provide Serologic Evidence of Elimination of Lymphatic Filariasis in The Gambia

Abstract. A current need in the global effort to eliminate lymphatic filariasis (LF) is the availability of reliable diagnostic tools that can be used to guide programmatic decisions, especially decisions made in the final stages of the program. This study conducted in The Gambia aimed to assess antifilarial antibody levels among populations living in historically highly LF-endemic areas and to evaluate the use of serologic tools to confirm the interruption of LF transmission. A total of 2,612 dried blood spots (DBSs) collected from individuals aged 1 year and above from 15 villages were tested for antibodies to Wb123 by enzyme-linked immunosorbent assay (ELISA). A subset of DBS (N = 599) was also tested for antibodies to Bm14 by ELISA. Overall, the prevalence of Wb123 was low (1.5%, 95% confidence interval [CI] 1.1–2.1%). In 7 of 15 villages (46.7%), there were no Wb123-positive individuals identified. Individuals with positive responses to Wb123 ranged in age from 3 to 100 years. Overall, Bm14 prevalence was also low (1.5%, 95% CI 0.7–2.8%). Bm14 positivity was significantly associated with older age (P < 0.001). The low levels of antibody responses to Wb123 observed in our study strongly suggest that sustainable LF transmission has likely ceased in The Gambia. In addition, our results support the conclusion that serologic tools can have a role in guiding programmatic decision making and supporting surveillance.