Abstract
There are at least 98 known pneumococcal serotypes. Invasive pneumococcal disease (IPD) is usually caused by a single serotype, and dual-serotype IPD is rare. To assess factors associated with dual-serotype IPD, patient information obtained through laboratory-based surveillance for IPD from 2005 through 2014 in South Africa was reviewed. Genomes of isolate pairs from coinfected individuals were sequenced to determine their molecular characteristics. For 30 (91%) of 33 patients with dual serotypes, one or both isolates were a pneumococcal conjugate vaccine (PCV13) serotype. Dual-serotype IPD was associated with children <5 years of age (adjusted odds ratio [aOR], 4.7; 95% confidence interval [95% CI], 1.8 to 11.7), underlying illness (other than HIV) (aOR, 2.8; 95% CI, 1.1 to 6.6) and death (aOR, 2.5; 95% CI, 1.08 to 6.09). For each coinfecting pair, isolates were genotypically unrelated, and their genotypes were common among isolates of the same serotype in South Africa. Of 701 accessory genes identified among dual-serotype IPD isolates, four were common between isolate pairs. Coinfecting isolate pairs had different genotypic backgrounds. The association of dual serotypes with death warrants increased awareness of IPD coinfection caused by two or more serotypes.