Streptococcal pharyngitis in schoolchildren in Bamako, Mali

Abstract

Background: Group A streptococcus (GAS) pharyngitis is associated with high rates of rheumatic heart disease in developing countries. We sought to identify guidelines for empiric treatment of pharyngitis in low-resource settings. To inform the design of GAS vaccines, we determined the emm types associated with pharyngitis among African schoolchildren.

Methods: Surveillance for pharyngitis was conducted among children 5-16 years of age attending schools in Bamako, Mali. Students were encouraged to visit a study clinician when they had a sore throat. Enrollees underwent evaluation and throat swab for isolation of GAS. Strains were emm typed by standard methods.

Results: GAS was isolated from 449 (25.5%) of the 1,759 sore throat episodes. Painful cervical adenopathy was identified in 403 children (89.8%) with GAS infection and was absent in 369 uninfected children (28.2%). Emm type was determined in 396 (88.2%) of the 449 culture-positive children; 70 types were represented and 14 types accounted for 49% of isolates. Based on the proportion of the 449 isolates bearing emm types included in the 30-valent vaccine (31.0%) plus nonvaccine types previously shown to react to vaccine-induced bactericidal antibodies (44.1%), the vaccine could protect against almost 75% of GAS infections among Bamako schoolchildren.

Conclusions: Two promising strategies could reduce rheumatic heart disease in low-resource settings. Administering antibiotics to children with sore throat and tender cervical adenopathy could treat most GAS-positive children while reducing use of unnecessary antibiotics for uninfected children. Broad coverage against M types associated with pharyngitis in Bamako schoolchildren might be achieved with the 30-valent GAS vaccine under development.

Figure 1

The number of patients with and without various clinical findings, alone or in combination, according to the presence of group A streptococcus (GAS) by throat culture. *5 findings denotes: tender cervical lymph nodes, tonsillar exudate, tonsillar hypertrophy, chills, or uvular erythema; **3 findings denotes: tender cervical lymph nodes, tonsillar exudate, or tonsillar hypertrophy; ‡2 findings denotes: tender cervical lymph nodes or tonsillar exudate.

Figure 2

The frequency of each emm type among the 396 isolates for which typing data was available. The first 14 types represent 49% of the isolates.

Figure 3

Of the 449 GAS isolates, 31% (indicated as VT or vaccine type) are included in the 30-valent vaccine presently under development. Based on data indicating that cross-coverage of certain emm types has been observed in-vitro (indicated as non-vaccine type killed, NVT-K), this vaccine could cover almost 75% of the Mali isolates. The vaccine does not cover 6.7% of isolates and there is no information regarding potential coverage of the remaining 18.3% (indicated as no data or no emm type).

Figure 4

Of the 70 emm types observed in Malian school children with pharyngitis, 19 types (VT) were among those covered by the 30-valent vaccine under development. Based on in vitro data, the 30-valent vaccine could induce cross-coverage of an additional 30 non-vaccine types (NVT-K). Six types (NVT-NK) would not be covered; there is no data on the coverage of the remaining 15 types observed.