Incidence of bacterial meningitis (2001-2005) in Lazio, Italy: the results of a integrated surveillance system

Abstract

Background: Monitoring the incidence of bacterial meningitis is important to plan and evaluate preventive policies. The study's aim was to estimate the incidence of bacterial meningitis by aetiological agent in the period 2001-2005, in Lazio Italy (5.3 mln inhabitants).

Methods: Data collected from four sources--hospital surveillance of bacterial meningitis, laboratory information system, the mandatory infectious diseases notifications, and hospital information system--were combined into a single archive.

Results: 944 cases were reported, 89% were classified as community acquired. S. pneumoniae was the most frequent aetiological agent in Lazio, followed by N. meningitis. Incidence of H. influenzae decreased during the period. 17% of the cases had an unknown aetiology and 13% unspecified bacteria. The overall incidence was 3.7/100,000. Children under 1 year were most affected (50.3/100,000), followed by 1-4 year olds (12.5/100,000). The percentage of meningitis due to aetiological agents included in the vaccine targets, not considering age, is 31%. Streptococcus spp. was the primary cause of meningitis in the first three months of life. The capture-recapture model estimated underreporting at 17.2% of the overall incidence.

Conclusion: Vaccine policies should be planned and monitored based on these results. The integrated surveillance system allowed us to observe a drop in H. influenzae b meningitis incidence consequent to the implementation of a mass vaccination of newborns.

Figure 1

Bacterial meningitis in Lazio, Italy, 2001–2005. Number of cases by place of birth and incidence by aetiological agent. 2a, the actual denominator of foreign-born people is not available, so only absolute numbers can be compared; 2b, in the incidence only residents of Lazio are included, independent of citizenship.

Figure 2

Bacterial meningitis in Lazio, Italy, 2001–2005. Seasonality by aetiological agent, for community acquired cases only.

Figure 3

Bacterial meningitis Case Fatality Rate by aetiological agent and age. The top of the figure reports the row CFR (%) for each aetiological agent, the expected number of deaths according to age-specific death rates for each age bracket, the standardised fatality ratio (i.e. observed deaths/expected deaths*100) and the relative confidence intervals. The graph reports age-specific fatality rates for all meningitis. The category "other" includes unknown aetiology. 2001–2005, Lazio, Italy.

Figure 4

Cases of bacterial meningitis in Lazio, Italy, 2001–2005. Results of the record linkage of the four data sources: hospital surveillance of bacterial meningitis (HSS), laboratory information system (LIS), the mandatory infectious diseases notifications (NDS), and hospital information system (HIS). The largest set includes the undetected cases as estimated by the capture-recapture model.