Streptococcus pneumoniae Invasive Disease, 2005
Statewide active surveillance for invasive Streptococcus pneumoniae (pneumococcal) disease began in 2002, expanded from the Twin Cities metropolitan area, where active surveillance has been ongoing since 1995. In 2005, 596 cases of invasive pneumococcal disease were reported, including 313 cases among Twin Cities metropolitan area residents, and 283 cases among residents of Greater Minnesota. Incidence rates overall, and by age group were similar between these two geographic regions. For example, there were 11.4 cases of invasive pneumococcal disease per 100,000 Twin Cities metropolitan area residents, and 11.9 cases per 100,000 residents of Greater Minnesota. By age group, annual incidence rates per 100,000 Twin Cities area residents and Greater Minnesota residents were, respectively, 27.4 and 21.3 cases among children aged 0-4 years; 3.6 and 3.5 cases among children and adults aged 5-39 years, 12.1 and 10.1 cases among adults 40-64 years, and 39.2 and 40.7 cases among adults aged 65 years and older.
In 2005, pneumonia accounted for 318 (53%) cases of invasive pneumococcal disease among all cases (i.e., those infections accompanied by bacteremia or isolation of pneumococci from another sterile site such as pleural fluid). The 170 pneumonia cases among Twin Cities area residents accounted for a similar proportion of all invasive disease in that group (54%) as the proportion among residents of Greater Minnesota (148 cases, 52%). Bacteremia without another focus of infection accounted for 211 (35%) cases statewide, including 103 (33%) cases in Twin Cities area residents and 108 (38%) cases in Greater Minnesota residents. Pneumococcal meningitis accounted for 30 (5%) cases statewide, including 14 (4%) of cases in Twin Cities area residents and 16 (6%) cases in Greater Minnesota residents. Forty-four patients with invasive pneumococcal disease died (7%); 6% (20) of case-patients who were Twin Cities area residents and 8% (24) of case-patients who were Greater Minnesota residents.
In 1999, the year before the pediatric pneumococcal conjugate vaccine (Prevnar, Wyeth-Lederle [PCV-7]) was licensed, the rate of invasive pneumococcal disease among children < 5 years in the Minneapolis-St. Paul metropolitan area was 111.7 cases/100,000. Over the years 2000-2002 there was a major downward trend in incidence in this age group (Figure 4). Compared with the lowest rate in 2002 (22.5 cases/100,000) the incidence rate in this age group increased slightly in the 3 following years, to 25.8 cases/100,000 in 2003, 29.0 cases/100,000 in 2004 and 27.4 cases/100,000 in 2005 (Figure 4). Based on the distribution of serotypes among isolates from these cases, this increase was limited to disease caused by non-vaccine serotypes (i.e. serotypes other than the seven included in PCV-7) (Figure 4). This small degree of replacement disease due to non-PCV-7 serotypes, similar to that seen in other parts of the country, has been far outweighed by the declines in disease caused by PCV-7 serotypes. This trend supports the need for ongoing monitoring, however, because further increases due to non-vaccine serotypes are possible. In Figure 3 rates of invasive pneumococcal disease among adults aged > 65 years are also shown by serotypes included and not included in PCV-7. Declines in incidence in this age group, particularly in disease due to PCV-7 serotypes have been observed elsewhere in the United States and are likely attributable to herd immunity from use of PCV-7 among children.
Of the 532 isolates submitted for 2005 cases, 46 (9%) were highly resistant to penicillin and 75 (14%) exhibited intermediate-level resistance; 92 isolates (17%) exhibited multi-drug resistance (i.e. high-level resistance to two or more drug classes). The proportion of isolates submitted from Greater Minnesota residents with high- or intermediate-level resistance to penicillin (48/235, 20%) was somewhat lower than the proportion from Twin Cities area residents (73/297, 25%) but the difference was not statistically significant. S. pneumoniae is one of several pathogens included in the MDH Antibiogram (see pages 49-50 of May/August 2005 DCN ), which gives detailed antimicrobial susceptibility results of isolates tested at the Public Health Laboratory from 2005 cases, and is available to download on the MDH Antibiogram website.