JUL 12, 2021 8:04 AM PDT

Do Asymptomatic Adults Harbor Strep?

WRITTEN BY: Carmen Leitch

Bacterial pathogens are thought to be a growing threat to public health. Streptococcus pneumoniae, for example, is most commonly found in kids and the elderly, but it's still a leading cause of community-acquired bacterial pneumonia in European adults. Not much is known about how it spreads among adults, but it's considered to be a potentially dangerous antibiotic-reistant pathogen. Scientists have now learned more about how S. pneumoniae can colonize the lungs of adults who don't show any symptoms. Colonization comes before disease, and is crucial for the transmission of a pathogen. The work has suggested that asymptomatic carriers appear to harbor the bacteria more often than we knew, and they may be spreading it.

A computer-generated illustration of a group of Gram-positive, Streptococcus pneumoniae bacteria based on SEM imagery and included in CDC's Antibiotic Resistance Threats in the United States, 2019  / Credit: CDC/ Antibiotic Resistance Coordination and Strategy Unit / Photo: Dan Higgins - Medical Illustrator

Reporting in Journal of Infectious Diseases, scientists observed a group of 87 Portuguese volunteers aged 25 to 50 years old for six months. Swabs were taken from multiple sites several times; oral, nasal, and throat samples were taken periodically and then tested to detect even low levels of S. pneumoniae microbes.

The work revealed that healthy adults are colonized with  S. pneumoniae relatively frequently. "The risk of an adult being colonized with pneumococci at least once during a period of one year was 57.5 percent,"said study co-author Ana Cristina Paulo. The median time of colonization was about two months, which is also longer than previous studies have indicated. Some adults were colonized with the  S. pneumoniae for all six months of the study. Though adults who lived with kids had a higher risk of having a positive S. pneumoniae test, how long it was carried did not depend on contact with children.

It seems that some adults may be acting as reservoirs of  S. pneumoniae. This study did not assess other bacterial pathogens that can cause pneumonia. Communities are protected from this disease in part because of vaccinations in children. But this study suggested that herd immunity may be variable if adults can harbor microbes that cause bacterial pneumonia.

"These outcomes are central when designing strategies to prevent pneumococcal disease in adults. By understanding this dynamic, we can contribute to public health decisions," said study leader Raquel Sá-Leão, Ph.D., of ITQB NOVA

Recently, a team of scientists have reiterated that they've been warning the world about a potential onslaught of antibiotic-resistant microbes. There is major concern that not enough attention has been paid to the problem.

"Time and again, the alarm bells have sounded for the broken antibiotic market. Compared to $8 billion of profit for cancer drugs, the $100 million loss for antimicrobials means that our medicine cabinets are becoming emptier - because of bankruptcies, not lack of scientific brainpower," explained Professor Dame Sally Davies, former Chief Medical Officer for England. "I have been saying that 'there is no time to wait,' but for many it is already too late; they have died. Unless we act now, the alarm bells will soon turn into the death knell for modern medicine,"

But experts also believe that it's still possible to prevent a disaster, as long as there is a global commitment to addressing the problem. The PASTEUR Act is pending in the US Congress. It aims to provide monetary incentives to developing antibiotics, and it may be a step in the right direction.

Sources: AAAS/Eurekalert! via Instituto de Tecnologia Química e Biológica António Xavier da Universidade NOVA de Lisboa ITQB NOVA, European Society of Clinical Microbiology and Infectious Diseases, Journal of Infectious Diseases

About the Author
  • Experienced research scientist and technical expert with authorships on over 30 peer-reviewed publications, traveler to over 70 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
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