Pneumonia with empyema and/or bacteraemia, febrile bacteraemia and meningitis are the commonest manifestations of invasive pneumococcal infection. Pneumococci (Streptococcus pneumoniae) are a frequent cause of non-bacteraemic pneumonia. In developing countries, non-bacteraemic pneumonia causes the majority of pneumococcal deaths in children. Middle-ear infections, sinusitis and bronchitis are non-invasive and less severe manifestations of pneumococcal infection, but are considerably more common. Several chronic conditions predispose to serious pneumococcal disease. Increasing pneumococcal resistance to antibiotics underlines the importance of vaccination.
Pneumococcal infection is a major cause of morbidity and mortality worldwide. In 2014, the WHO has estimated more than 1 million deaths were caused by this agent annually; this estimate included the deaths of 0.7–1 million children aged under 5 years. Most of these deaths occurred in poor countries and included a disproportionate number of children under the age of 2 years. In Europe and the USA, S. pneumoniae is the most common cause of community-acquired bacterial pneumonia in adults. In these regions, the annual incidence of invasive pneumococcal disease ranges from 10 to 100 cases per 100 000 population, in any range of age, including the population of over 65.
Meningococcal disease, also referred to as cerebrospinal meningitis is a contagious bacterial disease caused by the meningococcus (Neisseria meningitidis). It is spread by person-to-person contact through respiratory droplets of infected people. There are 3 main clinical forms of the disease: the meningeal syndrome, Pneumonia and systemic sepsis.. The onset of symptoms is sudden and death can follow within hours. In as many as 10-15% of survivors, there are persistent neurological defects, including hearing loss, speech disorders, loss of limbs, mental retardation and paralysis.
Neisseria meningitidis inhabits the mucosal membrane of the nose and throat, where it usually causes no harm. Up to 5-10% of a population may be asymptomatic carriers. These carriers are crucial to the spread of the disease as most cases are acquired through exposure to asymptomatic carriers. Waning immunity among the population against a particular strain favours epidemics, as do overcrowding and climatic conditions such as dry seasons or prolonged drought and dust storms. Smoking, mucosal lesions and concomitant respiratory infections are considered risk factors that may contribute to the development of the disease. The disease mainly affects young children, but is also common in older children and young adults.
The disease occurs sporadically throughout the world with seasonal variations and accounts for a proportion of endemic bacterial meningitis. However, the highest burden of the disease is due to the cyclic epidemics occurring in the African meningitis belt.