Abstract
Invasive meningococcal disease (IMD) is a serious, still feared and discussed disease, reaching a lethal rate of 8-15 % despite an early treatment initiation. The course of the disease is often peracute and, from the first signs of the disease, death can occur within 24-48 hours.
The source of infection is not only the manifestly ill individual but also the asymptotmatic carrier. Neisseria meningitidis, the causative agent of IMD, commonly colonises the upper respiratory tract, may occur in up to 10-15 % of the healthy population without causing any discomfort.
However, the prevalence of asymptomatic carriers in the population can be much higher, for example up to 35 % in areas with epidemic meningococcal disease. Age plays a major part in carriage.
Other risk factors increasing the likelihood of asymptomatic meningococcal carriage include male gender, active and passive smoking, concurrent bacterial or viral respiratory infection and long-term low socioeconomic status. The number of close social contacts (kissing each other and sharing objects such as glasses) also plays a role.
During adolescence, the prevalence of carriage gradually rises, peaking at around 19-25 years of age. Significant is its dramatic increase in college students, even during the first semester of study.
Meningococcal carrier strains do not belong to hypervirulent lines and an asymptomatic carrier is not at risk of developing IMD. But asymptomatic adolescents are the most common reservoir of infection.
Greater transmission of meningococcus among adolescents has been associated with an increase in the prevalence of meningococcal carriage in childhood and early adolescence and in the frequency of social contact. Elimination of risk factors and vaccination may help to guard against rising levels of the carriage.
MenACWY vaccines can prevent not only IMD infection, but also can reduce the prevalence of meningococcal carriage in the vaccinated population. In contrast, this effect is not clear for the MenB vaccine.