Communicable Diseases Epidemiological Report

DATA VALID EFFECTIVE March 2011

In this issue
CDER Editorial
Virological epidemiology of influenza infection in the African Region (2011)

Cholera situation in the first quarter of 2011 in the African Region

Clinical cases of yellow fever in the first quarter of 2011 in the African Region

Cerebrospinal meningitis in the first quarter of 2011 in the African Region

CDER Editorial Board
Dr F Kasolo
Dr Z Yoti
Dr B Impouma
Dr P Gaturuku
Dr A A Yahaya
Dr F Tshioko
Mr C Corera
Dr N Bakyaita Editor:
Dr J B Roungou, Director, DPC Cluster

Contact Information
WHO/AFRO, DPC Cluster
Attention: IDS
BP 6, Cite du Djoué, Brazzaville, CONGO
Tel: (242) 241 39387/39412 or (47) 241 38000
Fax: (47) 241 38005/6
Email: cder@afro.who.int
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CDER Editorial

Integrated Disease Surveillance and Response (IDSR) in the WHO African Region now goes beyond the scope of communicable diseases. Noncommunicable health conditions and events are also a priority in IDSR.

However, this March 2011 issue attempts to provide information on the burden of some of the regional priority communicable diseases such as cholera, cerebrospinal meningitis, influenza and yellow fever in the WHO African Region. The data presented were collected through the implementation of the Integrated Disease Surveillance Strategy in the region.

A number of questions remain unanswered in this report. What do the increased cholera and meningitis case-fatality rates (CFR) in the region tell us about the case management capacities of Member States? Is the apparent reduction in meningitis cases due to N. Meningitidis A (Nm A) in Burkina Faso, Mali and Niger a result of the recent introduction of the men A conjugate vaccine?

We hope you will find the contents of this report useful. Your comments and suggestions are most welcome and should be addressed to the Editor of the Communicable Diseases Epidemiological Report.

Dr J B Roungou
Director, DPC Cluster

Virological epidemiology of influenza infection in the African Region (2011)

There are 29 national influenza laboratories in the 24 countries of the WHO African Region responsible for providing information on the virological epidemiology of influenza in the region. These are members of the African Influenza Laboratory Network. The main goal of this network is to continue building the national laboratory capacity of African countries to conduct virological surveillance of viral respiratory diseases in general and influenza in particular. The primary laboratory diagnostic test used to generate virological information is the reverse transcriptase polymerase chain reaction (RT-PCR) technique. In addition to this test, 11 of the 24 countries also perform virus isolation.

During the first quarter of 2010, the network laboratories tested 11 353 specimens of which 2018 (18%) were positive compared with 9013 specimens tested in 2011 of which 1347 (15%) were positive. 1264 (63%) of the positive specimens were pandemic A (H1N1) in 2010 compared with 517 (38%) in 2011.

As shown in Figure 2, Pandemic A (H1N1) was the predominant influenza type during the first quarter of 2010 as opposed to the same period 2011, where both Pandemic A (H1N1) and seasonal influenza B were co-predominant. Overall there was a comparative drop in the number of Pandemic A (H1N1) cases in first quarter of 2011.

Cholera situation in the first quarter of 2011 in the African Region

By the end of the first quarter of 2011, 16 countries in the African Region had reported a total of 20 394 cholera cases with 406 deaths compared with 18 countries, 20 882 cases and 313 deaths in the corresponding quarter in 2010 as shown in Table 1 and Figure 3.

In 2011, countries reporting cases of cholera in the region continue to have an unacceptably high case-fatality rate, above the 1% threshold. High case-fatality rates may reflect the limited country preparedness to respond effectively to cholera outbreaks or an inability to detect cholera circulation at district level in good time.

Combating cholera calls for the development of comprehensive response plans that should include:

Recently, discussions have commenced on the possibility of using cholera vaccines as an additional tool in the fight of this disease (ref: WER No. 13, 2010, 85, 117–128).

Clinical cases of yellow fever in the first quarter of 2011 in the African Region

In first quarter of 2011, 11 countries reported 282 clinical cases of yellow fever with 11 deaths compared with 16 countries, 350 cases and 12 deaths recorded during the same period in 2010. The case-fatality rate for the suspected cases remained below the 4% threshold in both 2011 and 2010. Significant laboratory confirmed outbreaks were reported in Côte d'Ivoire and Uganda in 2011. The Uganda outbreak was unusual in that this was the first time in many years that yellow fever had been detected in the country.

Cerebrospinal meningitis in the first quarter of 2011 in the African Region

Figure 5 and Table 3 compare the burden of cerebral spinal meningitis during the first quarters of 2010 and 2011. A total of 20 countries reported cases of cerebrospinal meningitis in the first quarter of 2011 compared with 26 during the same period in 2010.

There were 9535 cases and 994 deaths attributable to cerebral spinal meningitis reported in the first quarter of 2011 compared with 15 003 cases and 1739 deaths in 2010 (see Table 3).

Cerebral spinal fluid (CSF) samples were collected, tested and reported on in countries with enhanced surveillance namely: Benin, Burkina Faso, Cameroon, Chad, Mali and Niger. During the first quarter of 2011, of the 1889 CSF samples tested, 757 were positive and overall the predominant pathogens were Streptococcus pneumoniae (47%), Neisseria meningitidis W135 (30%) and Neisseria meningitidis A (14%). During the same quarter of 2010, of the 1755 CSF samples tested, 843 were positive with Streptococcus pneumoniae (25%), Neisseria meningitidis A (30%) and Neisseria meningitidis W 135 (29%). (Refer to tables 4 and 5.) A significant observation is that there has been a decline in the overall confirmed cases of Neisseria meningitidis A in 2011. Of note is that before the meningitis season, the men A conjugate vaccine was introduced in Burkina Faso, Mali and Niger. Although it is early days, it is possible that this could be the reason for the drop in Neisseria meningitidis A related cases.

Country-specific reports on cerebral spinal meningitis

Burkina Faso, Mali and Niger located in the "meningitis belt" have been supported to conduct enhanced meningitis surveillance that includes monitoring cases and deaths as well as sero-typing the causative agents using polymerase chain reaction (PCR) techniques. Below we examine in more detail country specific reports from Burkina Faso, Niger and Mali using data in tables 3, 4 and 5.

Burkina Faso: The number of meningitis cases reported in the first quarter has decreased by 50% in 2011 (1903 cases and 340 deaths) when compared with 2010 (3827 cases and 544 deaths). Despite this there has been an increase in the case-fatality rates which went up slightly in 2011. In the first quarter 2011, Burkina Faso tested 857 samples of which 324 (38%) were positive for S. pneumoniae accounting for 79% of positive samples and Nm A only 0.6%. In the corresponding quarter of 2010, S. pneumoniae accounted for 53% of positive samples and Nm A 30%. There is a clear drop in the proportion of cases due to Nm A in 2011 compared with 2010 possibly related to the men A conjugate vaccine introduction.

Niger: Reported 676 cases and 78 deaths in the first quarter of 2011 compared with 1453 cases and 126 deaths in 2010, suggesting a 50% drop in both cases and deaths. In the first quarter of 2011, of the 484 specimens received, 236 (49%) were positive with the predominant pathogen being Nm W135 (79%), S. pneumoniae 16% and Nm A 1.3%. In the corresponding quarter 2010, the predominant pathogen was still Nm W135 (45%) followed by Nm A (27%). As is the case for Burkina Faso, the drop in proportion of positive specimens due to Nm A can be attributed to the partial introduction of men A conjugate vaccine.

Mali: In the first quarter of 2011 153 cases and 7 deaths were reported, compared with 238 cases and 16 deaths in the corresponding quarter of 2010. Of the 121 CSF samples received only 20 (16.5%) were positive with the predominant species Nm W135. In the corresponding period in 2010, only 6 samples were positive of which 4 were Nm A. Given the small sample sizes, it is difficult to interpret the trends.

Conclusion

Burkina Faso, Mali and Niger have recently introduced the men A conjugate vaccine. The first vaccination campaigns were conducted just before the beginning of the traditional meningitis season before December. The introduction of this vaccine may be responsible for the reduction in the number of Nm A cases in these countries. However, more data and analysis are needed to confirm the apparent decline.