Epidemiology,antibiotic susceptibility,and serotype distribution of Streptococcus pneumoniae associated with invasive pneumococcal disease in British Columbia - A call to strengthen public health pneumococcal immunization programs

BACKGROUND:

This study examined the epidemiology, antibiotic susceptibility and serotype distribution of Streptococcus pneumoniae associated with invasive pneumococcal disease (IPD) in British Columbia.

METHODS:

Six hospitals and one private laboratory network participated in a prospective, sentinel laboratory based surveillance study of IPD, between October 1999 and October 2000. At each site, S pneumoniae isolates were collected and epidemiological data were gathered using a structured questionnaire, for all cases of IPD meeting the study case definition. Isolates were serotyped and tested for antimicrobial susceptibility. Bivariate associations were analyzed and multivariate logistic regression was used to identify independent risk factors associated with hospitalization or death.

RESULTS:

One hundred three reports and isolates were collected. Seventy-nine per cent of cases were community-acquired, 64% required hospitalization and 5% died. Cases with one or more assessed risk factor for IPD and of female sex were independent variables associated with hospitalization or death. One-third of isolates had reduced penicillin susceptibility and 96% of these represented serotypes contained in the 23-valent pneumococcal polysaccharide vaccine (PPV-23). Overall, 89% of serotypes identified are included in the PPV-23 vaccine and 88% of isolates from children under five years of age are found in the 7-valent pneumococcal conjugate vaccine (PCV-7). Forty-one per cent of cases qualified for publicly funded pneumococcal vaccine and 34% of eligible persons were vaccinated.

CONCLUSIONS:

Overall, pneumococcal serotypes associated with IPD in this study closely matched serotypes included in PPV-23 products currently licensed in Canada. Most serotypes associated with IPD in children under five years of age are included in a recently licenced PCV-7. One third of isolates demonstrated reduced penicillin susceptibility, most involving serotypes included in PPV-23. Effective delivery of current public health immunization programs using PPV-23 and extending protection to infants and young children using the PCV-7 will prevent many cases of IPD.Key Words: Antibiotic susceptibility, Immunization, Serotype, Streptococcus pneumoniaeStreptococcus pneumoniae (pneumococcus) is a leading cause of invasive bacterial infections, including septicemia and meningitis, as well as non-invasive infections such as community-acquired pneumonia and acute otitis media (1-3). The highest rates of invasive pneumococcal disease (IPD) are seen in children under two years of age, in whom it is currently the leading cause of invasive bacterial disease in Canada and the United States (3,4). IPD is also a leading cause of illness and death among the elderly and persons having underlying chronic medical conditions (1,2,5). Overall, IPD accounts for more deaths in Canada and the United States than any other vaccine-preventable bacterial disease (6,7).Data from the Canadian National Centre for Streptococcus indicate the proportion of invasive pneumococcal isolates with reduced penicillin susceptibility increased from 5.5% to 15.2% between 1992 and 2000 (8). The Canadian Bacterial Surveillance Network has documented a similar trend of decreasing susceptibility to penicillin and to other antibiotics among pneumococcal isolates recovered from invasive, respiratory and other sites, between 1988 and 2001 (9).The high population burden of IPD and adverse consequences of increasing antimicrobial resistance of pneumococcus causing IPD give new impetus to public health prevention programs that better exploit the potential benefits of pneumococcal immunization (1,2,10). Only within the past five years has British Columbia, along with other Canadian provinces and territories, begun to offer 23-valent pneumococcal polysaccharide vaccine (PPV-23) through public health immunization programs, according to recommendations of the National Advisory Committee on Immunization (NACI). NACI recommends immunization using PPV-23 for all persons 65 years of age and older, and for those two to 64 years of age with health conditions placing them at higher risk of IPD or its complications (2,5). Further benefits may accrue after provinces/territories introduce a 7-valent pneumococcal conjugate vaccine (PCV-7) that was licensed in Canada in June 2001, into routine universal infant immunization programs. This vaccine has demonstrated potential to decrease acute or recurrant otitis media associated with antibiotic-resistant pneumococcus; reduce carriage and spread of resistant pneumococci in community settings; and decrease antibiotic use (11).We report on a one year, prospective, sentinel laboratory-based study of IPD in British Columbia, Canada. The objectives were to characterize the epidemiology, antibiotic susceptibility and serotype distribution of S pneumoniae associated with IPD, and viewed in the context of existing and future public health prevention strategies.