Objective: To analyse the association between the behavior of meningococcal disease and influenza, using for this purpose population statistics for Spain for the period of 1964 to 1997.
Methods: Ecological study of the incidence of meningococcal disease and influenza in Spain from 1964 to 1997, inclusive. The study used weekly statistical data for these diseases supplied by the Compulsory Disease Reporting System (Enfermedades de Declaración Obligatoria, EDO). The deterministic component of the meningococcal disease and influenza series was studied by means of spectral analysis based on the Fast Fourier Transformation, and the non-deterministic component was studied using the ARIMA model. The Box-Jenkins method was used for pre-bleaching the series, and a cross-correlation was subsequently established between the residuals in order to detect the presence of any significant correlations between the meningococcal disease and influenza series.
Results: During the period from 1964 to 1997, the week that showed, on average, the greatest number of cases for the season was week 7 in the case of meningococcal disease and week 6 in the case of influenza. Spectral analysis of the meningococcal disease and influenza series clearly demonstrated the annual periodicity of both series, and periodicity of nearly 11 years for meningococcal disease and slightly over 10 years for influenza. When cross-correlation is established after prebleaching the series, positive correlations are obtained in the results of lags 0, 1, 2, and 3. Introducing influenza as an exogenous variable in the multivariate model of meningococcal disease corroborates these results. There was a statistically significant relationship between the two processes during the same week and with a three-week lapse.
Conclusions: By means of a methodology not previously applied to this subject, and by the use of prolonged time-span, country-comprehensive population statistics (which includes several epidemics waves), an association was shown to exist between meningococcal disease and influenza. This suggests the need for the surveillance of the two processes in an interrelated manner.