Serotype 3 Remains the Leading Cause of Invasive Pneumococcal Disease in Adults in Portugal (2012-2014) Despite Continued Reductions in Other 13-Valent Conjugate Vaccine Serotypes

Abstract

Since 2010 the 13-valent pneumococcal conjugate vaccine (PCV13) replaced the 7-valent vaccine (PCV7) as the leading pneumococcal vaccine used in children through the private sector. Although, neither of the PCVs were used significantly in adults, changes in adult invasive pneumococcal disease (IPD) were expected due to herd protection. We characterized n = 1163 isolates recovered from IPD in adults in 2012-2014 with the goal of documenting possible changes in serotype prevalence and antimicrobial resistance. Among the 54 different serotypes detected, the most frequent, accounting for half of all IPD, were serotypes: 3 (14%), 8 (11%), 19A (7%), 22F (7%), 14 (6%), and 7F (5%). The proportion of IPD caused by PCV7 serotypes remained stable during the study period (14%), but was smaller than in the previous period (19% in 2009-2011, p = 0.003). The proportion of IPD caused by PCV13 serotypes decreased from 51% in 2012 to 38% in 2014 (p < 0.001), mainly due to decreases in serotypes 7F and 19A. However, PCV13 serotype 3 remained relatively stable and the most frequent cause of adult IPD. Non-PCV13 serotypes continued the increase initiated in the late post-PCV7 period, with serotypes 8 and 22F being the most important emerging serotypes. Serotype 15A increased in 2012-2014 (0.7% to 3.5%, p = 0.011) and was strongly associated with antimicrobial resistance. However, the decreases in resistant isolates among serotypes 14 and 19A led to an overall decrease in penicillin non-susceptibility (from 17 to 13%, p = 0.174) and erythromycin resistance (from 19 to 13%, p = 0.034). Introduction of PCV13 in the NIP for children, as well as its availability for adults may further alter the serotypes causing IPD in adults in Portugal and lead to changes in the proportion of resistant isolates.

Keywords: Streptococcus pneumoniae; antimicrobial resistance; conjugate vaccines; invasive disease; polysaccharide vaccine; serotype.

Figure 1

Serotypes of isolates causing invasive pneumococcal disease in adult patients (≥18 years) in Portugal, 2012–2014. The number of isolates expressing each serotype in each of the age groups considered is indicated. Isolates recovered from patients 18–49 years are indicated by black triangles, from patients 50–64 years by open squares, and from patients ≥65 years by open circles. Isolates presenting both erythromycin resistance and penicillin non-susceptibility (EPNSP) are represented by black bars. Penicillin non-susceptible isolates (PNSP) are indicated by dark hatched bars. Erythromycin resistant pneumococci (ERP) are indicated by light hatched bars. Isolates susceptible to both penicillin and erythromycin are represented by white bars. The serotypes included in the seven-valent conjugate vaccine (PCV7) and in the 13-valent conjugate vaccine (PCV13) are indicated by the arrows. NVT, non-vaccine serotypes; PPV23, 23-valent polysaccharide vaccine.

Figure 2

Isolates expressing serotypes present in PPV23 but not included in conjugate vaccines causing invasive pneumococcal disease in adult patients (≥18 years) in Portugal, 2012–2014. See legend of Figure 1. Out of the 11 serotypes present in PPV23 but absent from PCV13, serotype 2 was not found in our collection.

Figure 3

Isolates expressing serotypes not included in any pneumococcal vaccine causing invasive pneumococcal disease in adult patients (≥18 years) in Portugal, 2012–2014. See legend of Figure 1. NT, non-typable. Isolates expressing serotype 25A and 38 could not be distinguished phenotypically and are represented together. Only serotypes including n > 3 isolates are discriminated.

Figure 4

Proportion of isolates expressing serotypes included in pneumococcal vaccines causing invasive pneumococcal disease in adult patients (≥18 years) in Portugal, 2008–2014. The data up to 2011 were presented previously (Horácio et al., 2012, 2013).