Disease
The term “pneumococcal disease” refers to a group of clinical conditions caused by the bacterium Streptococcus pneumoniae. Invasive pneumococcal infections include pneumonia, meningitis and febrile bacteraemia; the common non-invasive conditions include otitis media, sinusitis and bronchitis. Infection is acquired by direct person-to-person contact via respiratory droplets or oral contact. There are many healthy, asymptomatic carriers of the bacteria, but there is no animal reservoir or insect vector.
Several chronic conditions predispose to serious pneumococcal disease (see below). Increasing pneumococcal resistance to antibiotics underlines the importance of vaccination.
Occurrence
Pneumococcal diseases are a worldwide public health problem. S. pneumoniae is the leading cause of severe pneumonia in children under 5 years of age, causing 0.7 – 1 million deaths each year, mainly in developing countries. In industrialized countries, most pneumococcal disease occurs in the elderly.
Risk for travellers
While travel itself does not increase the risk of acquiring pneumococcal infection, access to optimal health care may be limited during travel, increasing the risk of poor outcomes should disease occur. Certain conditions predispose to complica113 tions of pneumococcal infections, including sickle-cell disease, other haemoglobinopathies, chronic renal failure, chronic liver disease, immunosuppression after organ transplantation and other etiological factors, asplenia and dysfunctional spleen, leaks of cerebrospinal fl uid, diabetes mellitus and HIV infection. Elderly individuals, especially those over 65 years of age, are also at increased risk for pneumococcal disease. Pneumococcal vaccine may be considered for travellers who belong to these high-risk groups.
Vaccine
The current 23-valent polysaccharide vaccine represents pneumococcal serotypes that are responsible for 90% of pneumococcal infections and is immunogenic in those over 2 years of age. Children under 2 years of age and immunocompromised individuals do not respond well to the vaccine. Vaccination provides a relative protection against invasive pneumococcal disease in healthy adults. Pneumococcal polysaccharide vaccine is often recommended for selected groups, over the age of 2 years, at increased risk of pneumococcal disease. In some countries, such as the United States, routine vaccination is recommended for everyone aged over 65 years.
A conjugate vaccine containing seven serotypes of the pneumococcus is now available and is safe and immunogenic also in infants and children under 2 years. This vaccine is recommended by WHO as part of routine immunization in infants and has been introduced in some countries. It is advisable that children be up to date with immunization, as per the national recommendations, before undertaking travel.