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Dynamics of penicillin-susceptible clones in invasive pneumococcal disease
B Henriques Normark1, M Kalin, A Ortqvist
1Department of Bacteriology, Swedish Institute for Infectious Disease Control, Solna, Sweden. Birgitta.Henriques@smi.ki.se
Abstract:
In a 10-year period, 1987-1997, there was a >4-fold increase in the rate of pneumococcal bacteremia in Sweden. Invasive pneumococcal isolates (n=1136), which were obtained from 18 Swedish clinical microbiology laboratories from 1987 through 1997, and other national and international isolates were serotyped, and their clonal relationships were determined by molecular typing. The increase in invasive pneumococcal disease in Sweden during this period was associated particularly with an increase in isolates of serotypes 1 and 14. A 3-fold increase of type 14 was seen from 1987 through 1992, and a 10-fold increase of type 1 occurred from 1992 through 1997. One dominating penicillin-susceptible clone of type 14 was responsible for the increase of type 14 during the first 5 years. This clone also was found in Canada and the United States and was shown by multilocus sequence typing to correspond to a previously identified hyper-virulent clone. A novel penicillin-susceptible clone of type 1, which was not found among invasive isolates from 1987 or 1992, was responsible for the increase of serotype 1 during the last 5 years. These results illustrate the ability of virulent penicillin-susceptible pneumococcal clones to emerge and spread rapidly within a country.
Insights
Pneumococcal bacteremia cases surged in Sweden, driven by specific virulent clones of serotypes 1 and 14. These penicillin-susceptible strains rapidly emerged and spread, highlighting a significant public health concern.
Area of Science:
- Microbiology
- Infectious Diseases
- Epidemiology
Background:
- Pneumococcal bacteremia rates showed a significant increase in Sweden between 1987 and 1997.
- This rise in invasive pneumococcal disease (IPD) was particularly linked to specific serotypes.
Purpose of the Study:
- To investigate the serotype distribution and clonal characteristics of invasive pneumococcal isolates in Sweden over a 10-year period.
- To identify the specific bacterial clones responsible for the observed increase in pneumococcal bacteremia.
Main Methods:
- Serotyping of 1136 invasive pneumococcal isolates collected from 18 Swedish laboratories (1987-1997).
- Molecular typing, including multilocus sequence typing (MLST), to determine clonal relationships.
- Comparison with national and international isolates.
Main Results:
- A greater than 4-fold increase in pneumococcal bacteremia was observed in Sweden from 1987-1997.
- Serotypes 1 and 14 were particularly associated with this increase, with type 14 rising 3-fold (1987-1992) and type 1 rising 10-fold (1992-1997).
- A dominant penicillin-susceptible clone of serotype 14, identified as a hyper-virulent clone also found internationally, drove the early increase. A novel penicillin-susceptible clone of serotype 1 emerged later, responsible for the surge in type 1.
Conclusions:
- Virulent, penicillin-susceptible pneumococcal clones possess the capacity for rapid emergence and dissemination within a population.
- The findings underscore the dynamic nature of invasive pneumococcal disease epidemiology and the importance of molecular surveillance.