Pneumococcal Carriage in the COVID-19 Era
—New research found that despite COVID-19-era precautions—including masking and social distancing—rates of pneumococcal carriage among older adults were similar to those reported in this population before the pandemic.
Mitigation efforts in response to the COVID-19 pandemic in the northern hemisphere in 2020–2021 coincided with the radically reduced transmission of other respiratory viruses, such as respiratory syncytial virus and influenza. In addition, according to the investigators of a newly published study on the persistence of pneumococcal carriage among older adults during the first year of the COVID-19 pandemic, rates of invasive pneumococcal disease (IPD) were very low in the spring of 2020 across all age groups, and infection rates didn’t reach typical levels again until spring or summer of 2021.1
Despite these low levels of disease, the investigators note that pneumococcal carriage prevalence in children was near normal levels during the same period. Young children—common carriers of pneumococcus in their upper respiratory tract—continued to be carriers in the 2020–2021 season, but they didn’t appear to be getting sick from the infection. The investigators theorize that the reduction in upper respiratory viral infections, coupled with reluctance to seek healthcare during the pandemic, reduced the prevalence of pediatric IPD. And, they say, mitigation efforts like social distancing and mask-wearing may have further reduced transmission from children to adults.
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An analysis of pneumococcal rates in older adults
In a collaborative research project between investigators at Yale University and Pfizer, Anne Wyllie, PhD, Yale School of Public Health, New Haven, Conn., and her colleagues looked at pneumococcal carriage rates between October 2020 and August 2021 among couples living in the Greater New Haven area who met the following criteria: were 60 or older, didn’t live with anyone younger than 60, and were participating in an ongoing longitudinal carriage study.1
Biweekly saliva samples (567 in total) and questionnaires were collected from 95 individuals—47 household pairs and 1 singleton—for a period of 10 weeks. Polymerase chain reaction (PCR) testing was done for pneumococcus-specific sequences piaB and lytA. Participants were considered positive for pneumococcal carriage when cycle threshold (Ct) values for piaB were ≤40. The questionnaires collected information on participants’ social activities, contacts, and medical history to gain insight into potential factors in the epidemiology of pneumococcal carriage in older individuals.
Of the 567 saliva samples collected, 7.1% tested positive for pneumococcus. This represented 22 of 95 (23.2%) individuals and 16 of 48 (33.3%) households. The investigators found that although the participants largely avoided social events during the study period, many did continue to have regular contact with children. Those with regular contact with kids 2 to 9 years old exhibited a carriage rate of 15.9%, versus 5.4% for those who didn’t have regular contact with preschool and elementary school-aged children.
The influence of respiratory viruses on pneumococcal carriage
The investigators were surprised by the pneumococcus carriage rates seen in this study. “We had thought that the SARS-CoV-2 transmission mitigation measures—social distancing, mask wearing, etc.—would also impact the transmission and therefore carriage rates of pneumococcus in older adults,” says Dr. Wyllie, the study’s lead investigator. “This proved true for the respiratory viruses that typically circulate.”
“Moreover,” she continues, “all around the world, rates of invasive pneumococcal disease have declined. Combined, this meant that we were surprised to find in the older adults who participated in our study that the rates of pneumococcal carriage were similar to those reported in older adults pre-pandemic.”
The study also confirmed that older adults who had regular contact with children had higher rates of pneumococcal carriage.
“While children have been considered to be the reservoir of pneumococcus in the population, responsible for driving transmission to older age groups, these findings add to the growing body of evidence actually demonstrating this,” Dr. Wyllie says. “Our observations, combined with others around the world who also noted that carriage persisted in children and how pneumococcal disease rates only increased following the increased circulation of respiratory viruses, really highlight the influence respiratory viruses have on pneumococcal disease. This could impact public health messaging through subsequent respiratory infection seasons, raising the awareness of risk of co-infection or secondary infection and steps to mitigate this, or recommendations regarding pneumococcal vaccination or treatment strategies.”
Opening the door to further research
Dr. Wyllie says that the current study wasn’t able to address certain questions that remain about transmission.
“We had hoped to have been able to better study acquisition of pneumococcus from the community, as well as transmission between household members,” she says. “It would be interesting to repeat this study with communities reopened to better explore the potential of pneumococcus-acquisition events from the community activities individuals participate in and how this compares to rates of acquisition from children.”
Dr. Wyllie says the return of the typical respiratory viruses will likely increase transmission between household members, concluding that “this would also be interesting to explore further, including how pneumococcal carriage itself changes over the course of virus infection and as infection resolves.”
NOTE: This study was performed as a collaborative research project between researchers at Yale School of Public Health and Pfizer.
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