Invasive pneumococcal disease in Argentina: a snapshot from a retrospective observational study on serotypes, antimicrobial resistance, and the potential impact of the COVID-19 pandemic (2018-2022)

Abstract

Background: Streptococcus pneumoniae is a leading cause of morbidity and mortality and poses a significant public health threat globally. This study aimed to characterise changes in serotype distribution, in vitro antimicrobial susceptibility, and the frequency of invasive pneumococcal disease (IPD) in paediatric and adult populations in Argentina during the pre-COVID (2018-2019) and post-COVID (2021-2022) eras.

Methods: We conducted a national laboratory-based surveillance study analysing 1304 S. pneumoniae isolates sourced from Argentina's National Surveillance Program for invasive pneumococcal disease. Isolates were stratified by age and serotype, with antimicrobial susceptibility evaluated where applicable.

Findings: A significant decrease in isolates was observed in 2020, followed by a resurgence beginning in 2021, peaking in 2022. The most prevalent serotypes in children (<5 years) over the past five years included 3 (11%; 54/494), 24F (8%; 39/494), 19A (7%; 35/494), 12F (6%; 30/494), and 14/23B (4%; 20/494). In adults (≥18 years), the leading serotypes were 3 (17%; 92/542), 8 (14%; 76/542), 7F (5%; 27/542), 9N (4%; 22/542), and 19A (4%; 22/542). Notably, antimicrobial resistance levels were significant, with children showing higher resistance rates (26% multidrug resistance) compared to adults (8%), Among PCV13 serotypes, 19A was predominantly associated with multidrug resistance, while non-PCV13 serogroup 24 was prevalent among resistant isolates.

Interpretation: The fluctuations in serotype circulation, particularly among children under five, suggest evolving dynamics post-COVID-19. Although it remains uncertain if these changes are directly linked to the pandemic or reflect broader trends, the data highlight an urgent need for continued surveillance and potential adaptations in vaccination strategies.

Funding: No funding was received for this study.

Keywords: Adults; Antimicrobial resistance; Conjugate vaccines; Invasive pneumococcal disease; Paediatrics; Pneumococcal serotypes; Streptococcus pneumoniae.

Fig. 1

(A) Waffle plot. Proportion of isolates by year according to the different age groups and Coronavirus Pandemic Timeline in Argentina. (B) Time series spanning from 2010 to 2022 of invasive pneumococcal isolates submitted to NRL. Submitted cases of invasive pneumococcal disease (solid lines) were plotted against the counterfactual number of cases predicted by lineal regression model (dashed lines) if the COVID-19 pandemic had not occurred. To ensure robustness, we extended the temporal range back to 2010. The grey shading depicts 95% prediction intervals.

Fig. 2

(A and B) Isolates contribution by each site. (C) Comparison between population distribution across the country and the isolates distribution submitted to the NRL. (D) Illustrates the 95% confidence intervals for the expected cases, calculated using the indirect standardization method. (E) % Cases per 100.000 inhabitants. Isolates adjusted by region.

Fig. 3

Simpson’s Diversity Index (SDI) point estimate of serotypes causing IPD by year and group age.

Fig. 4

Difference in proportion by age group between the pre-COVID-19 era (2018–2019) and the post-COVID-19 era (2021–2022).

Fig. 5

Distribution of serotypes (PCV13 and others) over the past five years across various age groups. The left panel shows the proportion (%) and count (n) of PCV13 serotypes for each period. The right panel offers a detailed breakdown of these proportions, with each box representing the percentage of each serotype during the respective periods. This panel also includes information on the serotypes covered by the new vaccines (PCV15 and PCV20) authorized in Argentina.

Fig. 6

Theoretical Coverage of PCV and PPSV23. Note that PPSV23 is displayed only for adults. (A–D) Illustrate the temporal coverage for each age group by year. The size of the bubbles and the colour gradient are closely linked, with larger bubbles in darker shades indicating higher values. Results from 2020 was not included in the final analysis. (E) Provides a more detailed analysis of the coverage, allowing for comparison between each vaccine within the specific age, along with the p-values from the Fisher’s exact test for each comparison.

Fig. 7

Serotype distribution of penicillin, erythromycin, tetracycline/doxycycline and cotrimoxazole resistant isolates in global, children <5 and adults ≥18 years old.

Fig. 8

Theoretical coverage of current and upcoming next-generation vaccines according to antimicrobial resistance.