Streptococcus pneumoniae (also known as pneumococcus)
Not well defined as colonization usually precedes invasive disease; may be as short as 1 to 3 days.
Presumably as long as pneumococci are carried in oro-nasal secretions in asymptomatic individuals (colonization usually lasts weeks to months); with penicillin treatment, persons infected with susceptible strains are rendered non- infectious within 24-48 hours.
Respiratory droplets and direct contact with respiratory secretions of an infected person (usually requires frequent or prolonged close contact).
S. pneumoniae is one of the most common causes of invasive infections such as bacteraemia, meningitis and bacteraemic pneumonia, and bacterial mucosal infections such as sinusitis and otitis media. Of the 91 pneumococcal serotypes, 23 account for the vast majority of invasive pneumococcal disease (IPD) in humans. The worldwide emergence of pneumococcal resistance to antibiotics, including beta- lactams, macrolides, tetracycline, cotrimoxazole and fluoroquinolones has been a considerable concern.
Invasive pneumococcal infection is defined as the isolation of S. pneumoniae from normally sterile sites such as blood, pleural fluid and cerebrospinal fluid (CSF). Pneumococcal pneumonia is considered an invasive disease but would be excluded if blood or pleural fluid cultures are sterile. Otitis media is not considered an invasive disease, but may be included if S. pneumoniae is isolated from normally sterile middle ear fluid.
In Singapore, the mean annual hospitalisation rate for IPD from 2000-2008 was 8.9 per 100,000 population (about 380 cases per year). A total of 157 deaths from IPD were reported during this period, of which 5 were under the age of 5 years. In 2009, there were 251 reported cases of IPD. Of these, 124 met the criteria for IPD. The highest incidence rate was in children < 5 years of age and the elderly aged 65 years and above. In children, serotypes 14, 6B, 23F, 19F, 6A and 19A were the most common strains isolated, and accounted for 89% of all invasive diseases in children <5 years old. However, in adults, isolate distribution was more spread out and common ones were 14, 3, 6B, 8 and 19F which accounted for 51% of all invasive diseases. Mean case fatality rates for IPD in single-centre series were 6.1% in children but rising to 30% in children with pneumococcal meningitis; while in adults, this was 21.4%.
A pneumococcal polysaccharide vaccine (23-valent or serotype) has been available locally since 1988. It was recommended for children >2 years old with risk factors for IPD and adults >65 years old, but its immunogenicity was fair and its uptake was very poor. However, it would cover 82.8% of IPD serotypes in adults. A highly immunogenic pneumococcal conjugate vaccine (7-valent) was licensed locally for children 6 weeks to 9 years old since 2002 but became commercially available locally only since late 2005, with uptake primarily in children <5years within the private sector. In November 2009, it became the 10th vaccine-preventable disease to be included in the National Childhood Immunization Programme.