Serotypes/groups distribution and antimicrobial resistance of invasive pneumococcal isolates: implications for vaccine strategies

Abstract

Based on the invasive pneumococcal isolates referred to reference laboratories in Scotland in 1988-99, we identified the distribution of serotypes/groups and their antimicrobial resistance patterns in order to evaluate the coverage of polysaccharide and the new pneumococcal conjugate vaccines. A total of 5659 invasive isolates were included. Of these, 5124 (90.5%) were blood isolates, 308 (5.5%) were CSF isolates, 143 (2.5%) were blood and CSF and 84 (1.5%) were other normally sterile isolates. The most prevalent 11 serotypes/groups were 14, 9, 19, 6, 23, 1, 3, 4, 7, 8 and 18, in numerical order. These accounted for 84% of total serotypes/groups. The serotypes/groups included in the 23 and 14-valent polysaccharide vaccines accounted for 96% and 88% of all isolates. Both vaccines accounted for 98% of penicillin non-susceptible and 100% of erythromycin non-susceptible isolates. The 7, 9, and 11-valent conjugate vaccines covered 61, 68 and 80% of invasive isolates respectively. The coverage of these vaccines was substantially higher in youngest age group with 84, 86 and 93% of invasive isolates in children < 2 years included in the 7, 9 and 11-valent conjugate vaccines compared with 58, 64 and 77% in adults > or = 65 years of age. The serotype/group distribution of invasive isolates in Scotland varied from year to year over the period 1993-9. The coverage of the 23-valent vaccine remained above 95% in each year but the coverage of the 7, 9 and 11-valent conjugate vaccines showed more marked fluctuation with coverage as low as 53, 60 and 75% in some years. Continued surveillance of invasive pneumococcal isolates is required to inform the development of appropriate vaccine strategies to prevent pneumococcal disease in Scotland.

Serotypes and Sequence Types of Pneumococci Causing Invasive Disease in Scotland Prior to the Introduction of Pneumococcal Conjugate Polysaccharide Vaccines

“…In the United States, the introduction of the heptavalent Pnc vaccine has resulted in a decline in IPD, particularly in individuals below the age of 2 years (22). In the present study, new Pnc vaccines provided 50.7 to 64.1% coverage for all age groups, a level of coverage lower than those previously reported in Scotland (14). However, this may be due to the improved surveillance which has taken place since 2001, which represents a true picture of circulating serotypes (13).…”

“…Obtaining accurate epidemiological information is therefore important and is even more necessary in the era of new conjugate vaccines. Some epidemiological information relating to pneumococcal infection in Scotland is available (14,15), but surveillance was enhanced in 1999, although molecular tools were not used immediately (13). Discriminating between different serotypes of pneumococci provides limited information on individual clones causing invasive pneumococcal disease (IPD), because a single serotype can include a number of genetically divergent clones due to horizontal transfer of the capsular genes into new lineages (1).…”

Invasive pneumococcal disease and the potential for prevention by vaccination in the United Kingdom

“…At risk groups previously identified include: children < 2 years, adults > 65 years and those with medical co-morbidity such as chronic lung, heart, liver or renal disease, diabetes mellitus, asplenia, or immunosuppression. 4 The 23-valent capsular polysaccharide vaccine covers 97% of invasive pneumococcal isolates in the UK, 5 but is not immunogenic in children < 2 years and provides no immunological memory. In addition, its efficacy in targeted groups is controversial, depending on study design and endpoints used.…”

Potential Impact of Conjugate Vaccine on the Incidence of Invasive Pneumococcal Disease among Children in Scotland

“…However, the majority of invasive and noninvasive diseases are associated with a much smaller number of serotypes. The surveillance of invasive pneumococcal disease (IPD) has improved substantially throughout the United Kingdom in recent years due to interest in the potential for new pneumococcal vaccines (10,16,24,25,30). There remains a considerable burden of IPD in the United Kingdom, particularly during the winter months, despite the availability of antibiotics and pneumococcal polysaccharide vaccines (PPVs) (16,24).…”