Expanding the definition beyond surveillance criteria reveals a large burden of osteomyelitis caused by group B Streptococcus in the United States Veterans Health Administration.

Background: Population-based surveillance studies may underestimate osteomyelitis caused by Group B Streptococcus (GBS). We analyzed cases of GBS osteomyelitis, including patients diagnosed using an expanded case definition that incorporates cultures from non-sterile sites, as well as cultures from normally sterile sites.

Methods: We retrospectively examined a cohort of veterans with the diagnosis of osteomyelitis between 2008 and 2017. Cases of definite GBS osteomyelitis required GBS isolation from normally sterile sites, (e.g., blood or bone). Cases of probable GBS osteomyelitis permitted GBS isolation from non-sterile sites (e.g., surgical sites, wounds). We compared comorbid conditions, lower extremity amputation and mortality rates in these groups.

Results: Among 1281 cases of GBS osteomyelitis, the median age was 63 years, 87% had diabetes mellitus and 37% had peripheral vascular disease. Similar characteristics were found in 768 (60%) cases classified as definite and 513 (40%) classified as probable GBS osteomyelitis. Polymicrobial infection was less frequent in patients with definite than with probable GBS osteomyelitis (45% vs. 85%; P < 0.001). Mortality rates within 1-year were similar for definite and probable GBS osteomyelitis (12% vs. 10%). Amputation within 1-year occurred in 21% of those with definite and 10% of those with probable GBS osteomyelitis of the lower extremity, with comparable rates in the subset with monomicrobial infection.

Conclusions: Expanding the definition of GBS osteomyelitis to include cases with cultures from non-sterile sites may be warranted, increasing the estimated burden of GBS osteomyelitis. This can help guide preventive efforts to reduce the impact of GBS osteomyelitis.