Microbiological and epidemiological investigation of the Neisseria meningitidis serogroup A epidemic in Niger in 2009: last wave before the introduction of the serogroup A meningococcal conjugate vaccine?

The 2009 meningitis season in Niger was characterized by an early onset, beginning in the very first weeks of the year and peaking from the 12th to the 15th week with 5655 clinical cases over the 4 weeks. From 1 January 2009 to 28 June 2009 (week 26), a total of 13,733 clinical cases of meningitis were reported to the national epidemiological surveillance system with a case-fatality rate of 4·2%. During the season 25 of the 42 health districts reached the epidemic threshold and 11 the alert threshold. Reactive mass vaccination campaigns involving a total of 5 166,741 doses of the polysaccharide meningococcal bivalent (A+C) vaccine progressively controlled the outbreak in most parts of the country. A total of 3755 cerebrospinal fluid samples representing 28·1% of the suspected meningitis cases were analysed. Serogroup A meningococci were the causative agent in 97·5% of the meningococcal cases. Multi-locus sequence typing of 26 meningococal serogroup A strains showed 25 sequence type (ST)7 and one ST2859, both sequence types belonging to the ST5 clonal complex (CC5) of subgroup III. This is the largest epidemic observed in Niger since those of 1995-1996 (59,948 notified cases) and 2000 (14,633 notified cases).

Field evaluation of rapid diagnostic tests for meningococcal meningitis in Niger.

OBJECTIVE: To evaluate dipstick rapid diagnostic tests (RDTs) for meningococcal meningitis in basic health facilities. METHODS: Health facility staff received a one-day training. During the meningitis season, they performed RDTs on cerebrospinal fluid (CSF) specimens from suspected cases of meningitis. A frozen aliquot of CSF was later tested using polymerase chain reaction (PCR) to establish the reference diagnosis. RDTs used in health facilities were archived to allow checking the concordance between reported diagnosis and observed results. Reported diagnosis was also compared to PCR diagnosis. A second RDT was performed on each CSF specimen at the reference laboratory. RESULTS: Using RDTs, health facilities reported 382 negative results (73.9%), 114 NmA (22.1%), 12 NmW135 (2.3%) and nine uninterpretable results (1.7%), the latter corresponding to the misuse of a reagent by three agents. The agreement between reported diagnosis and archived dipsticks was excellent (kappa = 0.98). The agreement between PCR diagnosis and reported RDTs results was strong (kappa = 0.82). In health facilities, the sensitivity of RDTs for N. meningitidis A was Se = 0.91. The kappa coefficient measuring the agreement between RDTs operated in the reference laboratory and RDTs operated in health facilities was kappa = 0.78. CONCLUSION: We confirmed that dipstick RDTs to identify N. meningitidis serogroups A, C, W135 and Y can be reliably operated by non-specialized staff in basic health facilities. RDTs proved very useful to recommend vaccination in NmA epidemics, and also to avoid vaccination in epidemics due to serogroups not included in vaccines (NmX).

High sensitivity and specificity of the Pastorex latex agglutination test for Neisseria meningitidis serogroup A during a clinical trial in Niger.

There is a great need for a rapid diagnostic test to guide vaccine choice during outbreaks of meningococcal meningitis in resource-poor countries. During a randomised clinical trial conducted during an epidemic of Neisseria meningitidis serogroup A in Niger in 2003, the sensitivity and specificity of the Pastorex latex agglutination test for this serogroup under optimal field conditions were assessed, using culture and/or PCR as the gold standard. Results from 484 samples showed a sensitivity of 88% (95% CI 85-91%) and a specificity of 93% (95% CI 90-95%). Pastorex could be a good alternative to current methods, as it can be performed in a local laboratory with rapid results and is highly specific. Sensitivity can be improved with prior microscopy where feasible. A study specifically to evaluate the Pastorex test under epidemic conditions, using laboratories with limited resources, is recommended.

[Prevalence of tuberculous meningitis in Niamey's Hospital, Niger]. / Prevalence de la méningite tuberculeuse a l'hôpital de Niamey, Niger.

Tuberculosis is hyperendemic in Niger. In Niamey between June 2002 and May 2004, 996 cerebro-spinal fluids (CSF) collected from meningitis suspected patients have been analysed by PCR for the detection of Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae: the aetiologic diagnosis was obtained for 208 cases (20.9%). The Mycobacterium tuberculosis PCR assay performed on the negative samples was positive for 4 CSF: 0.4% prevalence among suspected cases of meningitis or 1.9% among confirmed bacterial meningitis.

[Behaviour and HIV seroprevalence investigation in sex workers of Dirkou, Niger, 2002]. / Enquête comportementale et de séroprévalence du VIH chez les professionnelles du sexe de Dirkou, Niger, en 2002.

In the framework of the Human Immunodeficiency Virus (HIV) surveillance, seroprevalence and behavioural survey was conducted in 2002 in Dirkou, a place of concentration of female sex workers (FSW) in Niger The global HIV seroprevalence found was 50% (CI at 95%: 40.6-59.36%). The behavioural survey revealed that 98% of FSW had heard about HIV whereas 78.7% know at least one HIV transmission way and 76.9% know at least one HIV prevention means. Only 33.3% declared using condom, what show that sensitisation efforts are needed to induce a behaviour change in FSW and their clients.

Evaluation of the Pastorex meningitis kit for the rapid identification of Neisseria meningitidis serogroups A and W135.

The recent emergence of Neisseria meningitidis W135 as a cause of epidemic bacterial meningitis and the availability of a trivalent ACW135 vaccine have created a need for accurate and timely meningococcal serogroup determination for organization of epidemic vaccine response. The sensitivity and specificity of the Pastorex meningitis kit (Bio-Rad) to identify serogroups A and W135 in the African meningitis belt was assessed using PCR testing as the gold standard. The sensitivity and specificity for serogroups A and W135 were 87 and 85%, respectively, while the specificities were 93 and 97%. The positive and negative likelihood ratios for A were 12 and 0.14 and for W135 were 33 and 0.16. The positive and negative predictive values, computed to simulate an epidemic of meningococcal meningitis with an estimated 70% prevalence of N. meningitidis among suspected cases, were 97% and 75% for A and 99% and 73% for W135. In remote locations of the African meningitis belt, latex agglutination is the only currently available test that can rapidly determine meningococcal serogroup. This study showed that latex agglutination performs well and could be used during the epidemic season to determine appropriate vaccine response.

[The use of dried blood spots for HIV-antibody testing in Sahel]. / Dépistage du VIH en zone sahélienne a partir de sang séché sur sérobuvard.

Undertaking a HIV seroepidemiological survey in Sahel is logistically problematic, since countries like Niger or Mali are very large with scattered populations and harsh climatic conditions. Therefore, the replacement of serum samples by whole blood dried on filter papers has been studied for HIV-antibody testing with commercial kits that are commonly used. In Niger, two tests ELISA (Genscreen HIV1/2 version 2, Vironostika HIV Uni-Form II Ag/Ab) and two rapid tests (Determine HIV1/2 et Immunocomb II HIV1&2 Bispot) were used to compare the dried blood spots and serum samples from 43 control individuals. Both ELISAs gave an excellent correlation (r = 0.99 et r = 0.98) between the dried blood spots and serum absorbance values. Using the rapid tests, the HIV status was found 100% concordant with dried blood spots and serum samples. An algorithm using three out of the four mentioned tests was defined then validated on the dried blood spots of 163 control individuals (100% concordant). In conclusion, dried blood spots may accurately and profitably replace serum samples for the serodiagnosis of HIV infection and for mass serosurveys in Sahel.

Nationwide HIV prevalence survey in general population in Niger.

A national population-based survey was carried out in Niger in 2002 to assess HIV prevalence in the population aged 15-49 years. A two-stage cluster sampling was used and the blood specimens were collected on filter paper and tested according to an algorithm involving up to three diagnostic tests whenever appropriate. Testing was unlinked and anonymous. The refusal rate was 1.1% and 6056 blood samples were available for analysis. The adjusted prevalence of HIV was 0.87% (95% CI, 0.5-1.3%) and the 95% CI of the estimated number of infected individuals was 22 864-59 640. HIV-1 and HIV-2 represented, respectively, 95.6% and 2.9% of infections while dual infections represented 1.5%. HIV positivity rate was 1.0% in women and 0.7% in men. It was significantly higher among urban populations than among rural ones (respectively, 2.1% and 0.6%, P < 10(-6)). Using logistic regression, the variables significantly related to the risk of being tested positive for HIV were urban housing, increasing age and being either widowed or divorced. The estimate from the national survey was lower than the prevalence assessed from antenatal clinic data (2.8% in 2001). In the future, the representativeness of sentinel sites should be improved by increasing the representation of rural areas accounting for more than 80% of the population. Compared with other sub-Saharan countries, the HIV prevalence in Niger is still moderate. This situation represents a strong argument for enhancing prevention programmes and makes realistic the projects promoting an access to potent antiretroviral therapies for the majority.

The oral route as a potential way of transmission of Schistosoma bovis in goats.

The infectivity of Schistosoma bovis cercariae administered orally was evaluated in Sahelian goats. Compared to the percutaneous route, a single massive oral dose resulted in a worm burden and in fecal egg excretion reduced by one-half. Surprisingly, tissue egg counts were increased by more than 4-fold. Fecundity of individual female schistosomes was, therefore, markedly increased. When infective doses were administered weekly for 20 wk, both worm and egg burdens were doubled without modification of the individual worm pair fecundity. Repeated oral infections seem to have induced an acquired tolerance toward parasite antigens. These results confirm the epidemiologic relevance of the oral route in a host species inclined to become infected through drinking water rather than percutaneous exposures.