Streptococcus pneumoniae Invasive Disease, 2002

In 2002, surveillance for invasive Streptococcus pneumoniae (pneumococcal) disease was expanded from the seven-county Twin Cities metropolitan area to include all counties statewide.

In 2002, 598 cases of invasive pneumococcal disease were reported in Minnesota, including 300 cases among residents of the Twin Cities metropolitan area and 298 cases in Greater Minnesota. Incidence rates of invasive pneumococcal disease were similar within each age group across geographic regions. For example, among infants less than 2 years of age, incidence rates per 100,000 population in the Twin Cities and Greater Minnesota were 32 and 36, respectively. Similarly, incidence rates in the Twin Cities and Greater Minnesota, respectively, were: 16 and 13 cases per 100,000 population among 2 to 4-year olds; 3 and 2 cases per 100,000 among 5 to 34-year-olds; 12 and 11 cases per 100,000 among 35 to 64-year-olds; and 40 and 44 cases per 100,000 among persons 65 years of age or older.

In 2002, pneumonia accounted for 333 (56%) cases of invasive pneumococcal disease (i.e., those infections accompanied by bacteremia or isolation of pneumococci from another sterile site such as pleural fluid). Pneumonia accounted for a somewhat higher proportion of cases in the Twin Cities (59%) than among cases in Greater Minnesota (52%). Bacteremia without another focus of infection accounted for 186 (31%) cases statewide, including 80 (27%) cases in Twin Cities area residents and 106 (36%) cases in Greater Minnesota. The proportions of cases attributed to pneumococcal meningitis (8%) and all other invasive infections (6%) were comparable in both geographic areas. Of the 598 cases of invasive pneumococcal disease, 69 (12%) patients died; fatality rates were similar in both residential groups.

Among 527 isolates submitted from cases reported in 2002, 64 (12%) were resistant to penicillin, and 38 (7%) exhibited intermediate susceptibility. The prevalence of penicillin resistance was identical in the Twin Cities and Greater Minnesota. Ninety (17%) isolates exhibited multidrug resistance (i.e., resistance to more than one drug class).

The 300 cases of invasive pneumococcal disease reported in the Twin Cities metropolitan area in 2002 represents a 12% decrease from the 340 cases reported in 2001. Incidence rates among infants less than 2 years of age declined most dramatically (Figure 5); this decrease is attributable to the use of the pediatric polysaccharide-protein conjugate vaccine (PCV-7) (Prevnar, Wyeth-Lederle) licensed in 2000. This vaccine covers seven of the pneumococcal serotypes that caused most of the invasive pneumococcal disease in children before PCV-7 was licensed. During 2002, only six (26%) of 23 invasive infections among children less than 2 years of age in the Twin Cities area were caused by serotypes covered by PCV-7, compared to 81% of 150 cases in 1999.

Consistent with findings elsewhere in the U.S., rates of invasive pneumococcal disease among persons 65 years of age or older decreased in the Twin Cities area in 2002. This decline may be due in part to the use of PCV-7 in children. Because PCV-7 reduces pneumococcal colonization by the vaccine serotypes in vacinees, the reservoir of circulating pneumococcal strains in the community may include fewer PCV-7 serotypes. Among case patients 65 years of age or older in 2002, 28 (28%) of 99 isolates were serotypes included in PCV-7, compared to 72 (51%) of 142 isolates in 1999. Conversely, it is not likely that this decrease reflects increased use of 23-valent pneumococcal polysaccharide vaccines (PPV-23, Pneumovax, Merck, and Pnu-Immune 23, Wyeth- Ayerst Laboratories) recommended for adults over 64 years of age and for other individuals with certain chronic conditions. Sixteen serotypes included in PPV-23 are not included in PCV-7. In 2002, 45 (45%) of 99 isolates from persons 65 years of age or older were among these 16 serotypes, compared with 42 (30%) of 142 isolates in 1999. Therefore, there was almost no change in the number of isolates with serotypes that were covered by PPV-23, except for those also covered by PCV- 7. Relatively mild influenza seasons in 2001-2002 and 2002-2003 also may have influenced the recent decline in pneumococcal disease in the elderly.

A decline in the proportion of antibiotic resistant pneumococcal strains among Twin Cities residents was observed in 2002, continuing a trend that began in 2001 (Figure 6). The prevalence of resistant pneumococcal strains has usually been higher in children less than 5 years of age than in other age groups. In 2002, five (12%) of 41 invasive isolates from children less than 5 years of age were penicillin-resistant, and eight (20%) of 41 isolates were resistant to more than one drug class. In comparison, among 133 isolates from this age group in 2000, 33 (25%) were penicillin-resistant and 44 (33%) were multi drug-resistant. An insignificant reduction in resistance has occurred among isolates from individuals 5 years of age or older. In 2002, 29 (12%) of 244 isolates from this age group were penicillin-resistant, and 43 (18%) were resistant to more than one drug class. In comparison, 35 (13%) of 277 isolates were penicillin-resistant, and 53 (19%) were multi drug-resistant in 2000. Due to declining invasive pneumococcal disease rates among young children, the absolute number of antibiotic-resistant isolates declined more quickly from 2000 through 2002 than did the proportion of resistant isolates (Figure 6). The seven serotypes included in PCV-7 represent the majority of antibiotic-resistant strains. Therefore, the decreased occurrence of resistant strains among invasive case isolates also may be attributed to increased use of PCV-7.

Additional information on antimicrobial susceptibility results for invasive pneumococcal isolates from 1996 through 2002 is available on the MDH website.

• For up to date information see>> Streptococcus pneumoniae (Pneumococcal Disease)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2002