Insights into seasonal dynamics of bacterial meningitis
Authors: Mustapha M Mustapha, Lee H Harrison
Journal: The Lancet Global Health (2016)

Despite remarkable progress in prevention via vaccines, bacterial meningitis remains a major global infectious disease challenge with high morbidity and mortality.1van de Beek D Progress and challenges in bacterial meningitis.Lancet. 2012; 380: 1623-1624Summary Full Text Full Text PDF PubMed Scopus (65) Google Scholar In this issue of The Lancet Global Health, Juliette Paireau and colleagues2Paireau J Chen A Broutin H Grenfell B Basta NE Global trends in seasonal dynamics of bacterial meningitis: a time-series analysis.Lancet Glob Health. 2016; 4: e370-e377Summary Full Text Full Text PDF PubMed Scopus (51) Google Scholar present a global meta-analytical study of the seasonal dynamics of three major pathogens that cause bacterial meningitis worldwide: Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. The study compiled a comprehensive global database of national meningitis surveillance data from 66 countries and analysed country-level data using innovative wavelet analysis. A distinct 12-month seasonal incidence pattern was detected in a remarkably consistent 96% of 38 countries that had sufficient data for analysis. Also, the study found a consistent relationship between the timing of peak bacterial meningitis incidence and latitude. Peak meningitis incidence was in February to March for countries in the meningitis belt of sub-Saharan Africa, with remaining countries having peaks in respective winter months in the northern and southern hemispheres. The same seasonal pattern persisted when meningitis surveillance data were broken down for all three species. The study did not find a difference in seasonality after introduction of new vaccines, despite a reduction in incidence. This is important because, although capsular group A epidemics seem to have been eliminated by introduction of the group A meningococcal conjugate vaccine in the meningitis belt, epidemics caused by group C, W, and X continue to occur there.3WHOMeningococcal disease control in countries of the African meningitis belt, 2014.Wkly Epidemiol Rec. 2015; 90: 123-131PubMed Google Scholar Since strain distribution undergoes frequent changes both because and independent of the impact of vaccination programmes, future analysis will be needed to assess whether changes in infecting strain affect the onset and peak meningitis incidence. Interestingly, there were some differences between seasonal peaks for the three pathogens in countries with such data. For example, in the four countries with both H influenzae and N meningitidis data, the N meningitidis peak preceded that of H influenzae by 3–6 weeks. Unexpectedly, the peak incidence of bacterial meningitis in Lebanon, a country with a Mediterranean climate, is in the hot and dry month of May, suggesting that some countries outside of sub-Saharan Africa may also have peak meningitis incidence associated with hot, dry weather. All three of these bacterial pathogens are transmitted via airborne respiratory droplets, colonise the pharyngeal mucosa, and reach the meninges through haematogenous spread.4Henriques-Normark B Tuomanen EI The pneumococcus: epidemiology, microbiology, and pathogenesis.Cold Spring Harb Perspect Med. 2013; 3: a010215Crossref Scopus (261) Google Scholar, 5Stephens DS Greenwood B Brandtzaeg P Epidemic meningitis, meningococcaemia, and Neisseria meningitidis.Lancet. 2007; 369: 2196-2210Summary Full Text Full Text PDF PubMed Scopus (737) Google Scholar Bacterial meningitis arises from an intricate interplay between host, pathogen, and environmental factors. On the bacterial side, recent studies applying high-resolution genomics have identified genetic factors that lead to the emergence of virulent pneumococcal and meningococcal strains predominantly through homologous recombination and phase variation within capsule-encoding and major antigen genes.6Lamelas A Harris SR Roltgen K et al.Emergence of a new epidemic Neisseria meningitidis serogroup A Clone in the African meningitis belt: high-resolution picture of genomic changes that mediate immune evasion.MBio. 2014; 5: e01974-e02014Crossref Scopus (45) Google Scholar, 7Mustapha MM Marsh JW Krauland MG et al.Genomic epidemiology of hypervirulent serogroup W, ST-11 Neisseria meningitidis.EBioMedicine. 2015; 2: 1447-1455Summary Full Text Full Text PDF PubMed Scopus (44) Google Scholar, 8Moore MR Gertz Jr, RE Woodbury RL et al.Population snapshot of emergent Streptococcus pneumoniae serotype 19A in the United States, 2005.J Infect Dis. 2008; 197: 1016-1027Crossref PubMed Scopus (437) Google Scholar Much is also known about host genetic and behavioural risk factors for bacterial meningitis.5Stephens DS Greenwood B Brandtzaeg P Epidemic meningitis, meningococcaemia, and Neisseria meningitidis.Lancet. 2007; 369: 2196-2210Summary Full Text Full Text PDF PubMed Scopus (737) Google Scholar Even though the seasonal nature of meningitis has been known since at least the 1960s,9Lapeyssonnie L Comparative epidemiologic study of meningococcic cerebrospinal meningitis in temperate regions and in the meningitis belt in Africa. Attempt at synthesis.Med Trop (Mars). 1968; 28: 709-720PubMed Google Scholar the exact mechanisms by which environmental factors exert a seasonal influence on incidence remain unclear. The majority of the meningitis belt lies within an area with 300–1100 mm annual rainfall that experiences large meningococcal epidemics in the dry and dusty months of February to April.3WHOMeningococcal disease control in countries of the African meningitis belt, 2014.Wkly Epidemiol Rec. 2015; 90: 123-131PubMed Google Scholar Meningococcal cases typically show a precipitous decline with the onset of the rainy season. Physical damage to pharyngeal mucosa, concomitant viral infections, and changes in normal pharyngeal flora have been proposed, although not yet established, as the cause of these dramatic changes in incidence.5Stephens DS Greenwood B Brandtzaeg P Epidemic meningitis, meningococcaemia, and Neisseria meningitidis.Lancet. 2007; 369: 2196-2210Summary Full Text Full Text PDF PubMed Scopus (737) Google Scholar, 10Brundage JF Interactions between influenza and bacterial respiratory pathogens: implications for pandemic preparedness.Lancet Infect Dis. 2006; 6: 303-312Summary Full Text Full Text PDF PubMed Scopus (309) Google Scholar What are the public health implications of Paireau and colleagues' study? First, it demonstrates the utility of large global databases to address fundamental questions about infectious diseases epidemiology. In this case, the data are from national surveillance systems, which further underscores the value of public health surveillance. In that regard, the study highlights the need for strengthened meningitis surveillance in countries with limited data such as India, parts of the Middle East, and central Asia, primarily to measure disease burden and formulate vaccination policy. Second, an improved understanding of the complex interplay of environmental forces in the pathogenesis of bacterial meningitis could help in public health preparedness, especially for the 19 meningitis belt countries in Africa that experience meningococcal epidemics.3WHOMeningococcal disease control in countries of the African meningitis belt, 2014.Wkly Epidemiol Rec. 2015; 90: 123-131PubMed Google Scholar Third, it will be important to determine whether the seasonal dynamics demonstrated in this study will change in the setting of ongoing climate change. In summary, Paireau and colleagues present important groundwork on global seasonal dynamics of bacterial meningitis. How complex environmental variables, the natural dynamics of bacterial meningitis, and immunisation programmes will affect seasonal and long-term temporal changes in bacterial meningitis epidemiology warrants additional investigation. We declare no competing interests. Seasonal dynamics of bacterial meningitis: a time-series analysisOur findings provide key insight into the seasonal dynamics of bacterial meningitis and add to knowledge about the global epidemiology of meningitis and the host, environment, and pathogen characteristics driving these patterns. Comprehensive understanding of global seasonal trends in meningitis could be used to design more effective prevention and control strategies. Full-Text PDF Open Access