By Javairia Khalid, Lecturer, The Aga Khan University, Pakistan
Group B streptococcus (GBS) or Streptococcus agalactiae is a type of bacteria that commonly inhabits the gastrointestinal and genital tracts of healthy individuals. While it is a commensal organism in most situations, certain conditions can cause GBS to become pathogenic and result in disease. GBS is a well-characterised pathogen in infants and pregnant women, but it has increasingly been observed causing invasive infections in non-pregnant adults, including skin or soft-tissue infections, urinary tract infections, pneumonia, bacteraemia with no identified focus, arthritis, osteomyelitis, meningitis and endocarditis. The incidence of invasive S. agalactiae infections in non-pregnant adults is estimated to be approximately 11 per 100,000 patients with underlying medical conditions such as diabetes mellitus or neoplasia being more susceptible. During 2015–2016, a total of 3,156 episodes of invasive group B Streptococcus (iGBS) infection in adults (>15 years of age) were recorded in England, corresponding to an annual incidence of 3.48/100,000 population.
Despite being a less common pathogen in non-pregnant adults, the increasing incidence of invasive Group B Streptococcus infection among this population has become a major health concern. One of the notable factors that make Group B streptococcus infections in non-pregnant adults a critical health concern is the severity and varied natureof clinical manifestations it can cause. Skin or soft-tissue infections are among the most common clinical manifestations of GBS in non-pregnant adults and often present in the form of cellulitis, abscesses, or wound infections. Urinary tract infections caused by GBS in non-pregnant adults are usually uncomplicated cystitis, although they can lead to pyelonephritis and bacteraemia in some cases. Pneumonia caused by GBS in non-pregnant adults can present with lobar consolidation or bronchopneumonia and may be associated with sepsis.
GBS infections in non-pregnant adults have been recognised since 1940, but their burden is considerable and still increasing. They are associated with a higher mortality rate than GBS infections in pregnant women due to delayed diagnosis and underestimation of the significance of the symptoms. Adults 65 years or older are at increased risk compared to adults younger than 65 years old. GBS also causes many non-invasive diseases so the overall burden in adults is likely to be much higher. This highlights the importance of recognising GBS as a potential pathogen causing disease even if risk factors are not present or blood and joint cultures come back negative.
Most nonpregnant adults have emergency cases, and all-cause mortality is high (one quarter of cases). Early recognition of infection, a search for deep-seated infection, appropriate antimicrobial therapy, and in some cases concomitant surgical intervention are essential elements of successful management of GBS disease. Ongoing monitoring of serotype distribution and antibiotic resistance is warranted and reducing risk factors through hygienic-dietary parameters and maintaining skin integrity may help towards the prevention of invasive GBS infections. If rates of disease continue to climb, prevention efforts for adults will take on greater priority especially the potential for prevention of GBS through vaccination.