An attempt at an epidemiological explanation - Epib.nl

Chapter 1Meningococcal disease (MD) is a serious illness caused by Neisseria meningitidis(meningococcus). The clinical spectrum of MD ranges from a relatively barmless flulikesyndrome to meningitis and fulminant septic sbock with fatal ou tcome. Theoccurrence of cases of MD in rapid succession generally leads to public alarm.Because of the severity of the disease and the threat of an epidemic, MD must benotified to the bealth authorities in many countries.Since 1958, isolates of N. meningitidis recovered from patients with MD in theNetherlands have been forwarded to the Netherlands Reference Laboratory fo rBacterial Meningitis (RLBM) of the Department of Medical Microbiology, Universityof Amsterdam, and the National Institute for Public Health and EnvironmentalProtection by almost all Dutch clinical microbiological laboratories. The isolates arestored at _70°C, and are readily available for further researcb. The collectioncurrently comprises over 7000 meningococcal isolates, and is of great value for fundamentaland epidemiological researcb. From 1982 onwards, a gradual increase in tbenumber of submissions of meningococcal isolates to the RLBM was noted, and in1988 the incidence of MD in the Netherlands reacbed a sub-epidemic level. In 1989 itwas decided to conduct a nation-wide survey on MD. This thesis addresses variousepidemiological aspects of this survey. In this introductory cbapter some generalfeatures of N. meningitidis and MD are described, as well as aspects of the preventionof MD. Finally, the objectives of the study and tbe contents of this thesis areindicated.Neisseria meningitidisBacterio[ogrN. meningitidis is a gram-negative diplococcus, whicb can be directly visualized ingram-stains of the cerebrospinal fluid, fluid from petechial lesions or the buffy-coat ofthe peripheral blood of infected patients.' The organism grows easily on variousmedia, such as blood agar and cbocolate agar.' Optimal growth is achieved in a moistenvironment at 35-37°C under an atmosphere of 5-10% CO,.' N. meningitidis can bedistinguished from other Neisseria species, like Neisseria [actamica and Neisseriagonorrhoeae, on the basis of its sugar metabolism.'Among the principal surface structures of N. meningitidis are pili, or fimbriae, thecapsule and the outer membrane." Pili are finger-like surface appendages whicb playan important role in the attachment of N. meningitidis to the mucosal surface of tbenasopbarynx. Pili sbow marked intra and interstrain variability, both quantitativelyand qualitatively. The majority of meningococci isolated from patients with MDproduce a polysaccharide capsule, whicb is considered as a virulence property,because it allows the meningococcus to evade host defense mechanisms and tosurvive in the bloodstream of tbe host.' Directly underneath the capsule lies the outermembrane, whicb contains a number of proteins and lipopolysaccbarides' 4 5 Based ontheir molecular weigbts, tbe major outer membrane proteins (OMPs) are categorized4