WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - Meningococcal disease
China and Nigeria (Table 5.1) reported the highest number of cases between 1966 and 1998. Almost all major epidemics in terms of numbers of cases in this period occurred in the meningitis belt. Poland (27 569 cases in 1972), India, the Russian Federation and China (over 100 000 cases in 1979 and 1980), are among the countries that had high numbers of cases and are located outside the meningitis belt.
The length of the epidemic cycles are not the same for all countries in the meningitis belt (Fig. 5.1), Niger and Nigeria: 8-9 years, Burkina Faso: 10-15 years, Sudan: 10 years.
The last two epidemics in Ethiopia were proceeded within two to three years by an epidemic in Sudan (Fig. 5.1). It is expected that Ethiopia will soon have an outbreak of meningococcal disease, given the outbreak of Sudan in 1999.
Fig. 5.1 Epidemic cycles, meningococcal disease for selected African countries,1996-1999
- The number of cases in the years immediately proceeding and following large epidemics are often elevated and sometimes reach epidemic levels. An example of this is Burkina Faso in the 1980s (Table 5.1 and Fig. 5.1).
- Some reports arrive late, when there are already a considerable number of cases. For example, Burkina Faso started reporting to WHO when there were already 383 cases (1996). An efficient early warning system would detect an elevated number of cases in the early stage of an epidemic (Fig. 5.2).
Fig. 5.2 Seasonality of epidemics of meningococcal disease, reported number of cases
per calendar week for selected epidemics in Africa, 1995-1999
- The reported case fatality rate is higher in the beginning of an epidemic than at the end. Apart from a genuine change caused by better treatment, a major reason for this is a change in reporting practices. At the start of an epidemic there is a tendency for underreporting of less severe cases and the reverse as the epidemic progresses (Fig. 5.3).