The prevalence of pneumococcal carriage in Serbia during COVID

By Dr. Sanchari Sinha Dutta, Ph.D.Oct 17 2022Reviewed by Benedette Cuffari, M.Sc.

In a recent PLoS One journal study, scientists explore the prevalence of Streptococcus pneumoniae (Spn) carriage and its antimicrobial resistance patterns in adults aged 50 years and older during the coronavirus disease 2019 (COVID-19) pandemic. Herein, a low prevalence of Spn carriage was observed, in addition to identifying four vaccine-related serotypes.

Study: Pneumococcal carriage in adults aged 50 years and older in outpatient health care facility during COVID-19 pandemic in Novi Sad, Serbia. Image Credit: Jezper / Shutterstock.com

Background

Carriage of Spn is associated with developing pneumococcal disease and pathogen transmission within the community. Meningitis, septicemia, pneumonia, sinusitis, and otitis media are common examples of pneumococcal disease.

A high prevalence of Spn carriage has been observed in children under two years; however, the pathogen can also infect adults of any age. The age distribution of the disease may vary between countries, depending on the socioeconomic status of the affected individual and environmental factors.

The implementation and evaluation of pneumococcal mass vaccination programs in developing countries significantly depend on the quality of epidemiological data on Spn carriage. For example, in Serbia, mass immunization with pneumococcal conjugated vaccines has reduced the prevalence of antibiotic-resistant serotypes and vaccine-specific serotypes. However, no surveillance system is available in the country to evaluate the long-term effectiveness of immunization programs.

In the current study, scientists determine Spn's prevalence and antibiotic-resistant patterns during the COVID-19 pandemic in middle-aged and older adults residing in Novi Sad, Serbia.

Study design

The study included 521 participants with or without upper respiratory tract infection symptoms who visited an outpatient facility during the second year of the COVID-19 pandemic.

One nasopharyngeal and one oropharyngeal sample were collected from each participant, totaling 1,042 samples. The samples were subjected to molecular serotyping and antibiotic-resistance testing.

Spn carriage serotypes  

All samples collected from the participants were cultured for the identification of Spn. Of 521 participants, only 16 exhibited the presence of Spn. This indicates a low Spn carriage prevalence of about 3% among study participants.

Molecular serotyping of the 16 Spn-positive samples identified four vaccine-specific serotypes and two non-vaccine serotypes. The remaining ten samples were non-typeable isolates of pneumococci.

Among the four vaccine-specific serotypes denoted as 6A, 11A, 15B, and 18C, 6A and 18C were related to the PCV13 vaccine, whereas 18C, 11A, and 15B were associated with the PPSV23 vaccine.   

Regarding seasonal variation, a significantly higher prevalence of Spn-positive samples was observed in May, June, October, and December compared to those obtained in July and September.   

Spn antibiotic-resistance patterns

All Spn-positive samples were subjected to antibiotic-resistance testing. The highest resistance of Spn was observed against erythromycin and tetracycline.

Erythromycin resistance was observed explicitly for one vaccine-specific and one non-vaccine serotype and eight non-typable samples. Additionally, two non-vaccine serotypes and five non-typable samples were resistant to tetracycline.  

None of the samples were resistant against ceftriaxone, trimethoprim/sulfamethoxazole, and levofloxacin, irrespective of the serotypes. In addition, multidrug resistance was observed for one non-vaccine serotype and two non-typable samples.

Study significance

The study provides an overview of Spn carriage during the COVID-19 pandemic in middle-aged and older adults residing in Serbia. Based on the study estimates, Serbia has a low prevalence of Spn carriage. All six Spn serotypes identified in the study were obtained from nasopharyngeal samples.

The majority of analyzed samples are non-typable, thus indicating the absence of polysaccharide capsules in these samples. Four vaccine-specific serotypes have been identified that were covered by the PCV13 and PPSV23 vaccines.

Although the scientists could not provide any definitive conclusion regarding the effects of pneumococcal vaccines on the prevalence and dynamics of Spn carriage, they highlight the need for increasing vaccine coverage among middle-aged and older adults in Serbia.

Regarding antibiotic resistance, the study finds that most Spn-positive samples are resistant to erythromycin and tetracycline. However, resistance against penicillin has rarely been observed in analyzed samples.