Streptococcus pneumoniae (S. pneumoniae) causes pneumococcal infections, it is an important bacterial pathogen causing a high burden of morbidity and mortality worldwide. There are more than 90 different strains (called serotypes) able to cause disease. The organism normally lives in the human nasopharynx and can cause either non-invasive disease (such as bronchitis, otitis media and sinusitis) or invasive pneumococcal disease (such as bacteraemia, septicaemia, osteomyelitis, pneumonia, meningitis and septic arthritis). Young and elderly people are at higher risk of disease (under 2 years and over 65 years of age), particularly if an individual is immunocompromised. The disease is seasonal with peaks particularly in winter months.
The Pneumococcal Surveillance Group has been collecting S. pneumoniae strains causing invasive disease in Oxford University Hospitals since 1995 and expanded to a further 8 hospitals (Stoke Mandeville Hospital, Milton Keynes General, Bedford Hospital, Kettering General, Royal Berkshire Hospital, Northampton General, Wycombe General and Wexham Park) in 1996, Southampton General Hospital in 2005 and the Royal Sussex County Hospital in Brighton in 2009.
We have collected nearly 6,000 strains in this time which includes more than 50 different serotypes. There has been a reduction in the incidence of invasive disease since the beginning of the work from 10/100,000 persons per year in 1996/1997 to 7/100,000 in 2012/2013. Declines were greater in children under two years of age (from 37/100,000 to 14/100,000 respectively). The incidence of disease in those covered by the vaccines declined significantly in all patients, however the number of infections caused by serotypes not contained in the vaccines have increased.
As the PCV13 has only been used in the UK since April 2010, ongoing surveillance such as ours is essential in examining the epidemiology of this disease.
We are using new technologies such as whole genome sequencing to interrogate the organism and have close collaborations with a number of groups across the world including Professor Anthony Scott based at the London School of Hygiene and Tropical Medicine and Kilifi in Kenya and Professor Samir Saha based in Dhaka Shishu Hospital, Bangladesh.
Vaccines and Treatment
Some of the serotypes are thought to cause more disease than others, therefore the vaccines produced have targeted these serotypes. There are two different kinds of vaccines available:
- the pneumococcal polysaccharide vaccine (PPV) which is given to people over 65 years of age, this vaccine contains 23 of the different serotypes
- the pneumococcal conjugate vaccine which is aimed at children under two years of age, the first preparation used in the UK contained 7 serotypes (PCV7) and the current vaccine in use contains 13 serotypes (PCV13) (http://www.nhs.uk/Conditions/vaccinations/Pages/pneumococcal-vaccination.aspx)
The introduction of these vaccines has reduced the burden of S. pneumoniae disease in the UK.
Non invasive disease is not normally treated as the disease is mild and self limiting, invasive disease is treated with antibiotics (http://www.nhs.uk/conditions/Antibiotics-penicillins/Pages/Introduction.aspx).