Background The value of positive follow-up blood cultures (FUBC) in streptococcal bacteremia has not been well-defined. We therefore explored the frequency of and risk factors for positive FUBC in a retrospective cohort of patients with streptococcal bacteremia. Methods Adults ≥ 18 years of age, admitted with at least one positive blood culture for Streptococcus spp. between 2013 and 2018 followed by at least one FUBC, were potentially eligible. Positive FUBC were defined as cultures positive for the same streptococcal species drawn > 24 hours after the index culture. We excluded patients with polymicrobial bacteremia. We compared the characteristics of patients with and without a positive FUBC. Results In our single-center cohort, we identified 590 patients with streptococcal bacteremia, 314 patients met inclusion criteria. Ten patients had FUBC with Streptococcus spp. (3.2%); 4 (1.3%) had a contaminant identified, and 3 (1.0%) had a new pathogen isolated. Endocarditis (5/10, 50.0% vs 35/304, 11.5%), epidural abscess (2/10, 20% vs 4/304, 1.3%) and discitis or vertebral osteomyelitis (3/10, 30.0% vs 14/304, 4.6%) were associated with positive FUBC. Patients with positive FUBC had a longer median length of stay (12.9 vs 7.1 days, p=0.004) and longer duration of antibiotic treatment (14.9 vs 43.2 days, p=0.03). Conclusions Follow-up blood cultures among patients with streptococcal BSI are rarely positive. Clinicians could consider limiting follow-up blood cultures in patients at low risk for deep-seated streptococcal infections, persistent bacteremia, or endovascular infection.

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In patients infected with human immunodeficiency virus (HIV), antiretroviral therapy has decreased the risk of progression to acquired immunodeficiency syndrome or death significantly. However, many individuals still present with an opportunistic infection as the first clinical manifestation of HIV infection. This complicates therapy due to frequent and complex drug interactions between antiretrovirals and the drugs used to treat the opportunistic infection. We describe a 48‐year‐old man coinfected with HIV and disseminated Mycobacterium avium complex (MAC). His treatment for MAC started about 2 weeks before he started antiretroviral therapy. The MAC regimen consisted of clarithromycin 500 mg/day, ethambutol 1200 mg/day, rifabutin 150 mg every other day, and ciprofloxacin 500 mg twice/day. His antiretroviral therapy consisted of atazanavir 300 mg/day, ritonavir 100 mg/day, and emtricitabine 200 mg‐tenofovir 300 mg/day. Approximately 95 days after receiving these concomitant therapies, his rifabutin peak concentration was 0.08 μg/ml (goal peak concentration > 0.45 μg/ml); thus, the dosage of rifabutin was increased to 300 mg every other day. Fourteen days later, his rifabutin peak concentration was 0.43 μg/ml. Drug interactions between antiretrovirals and antimycobacterials are complex and not fully understood in patients with HIV infection. Although the recommended dosage of rifabutin in patients receiving a ritonavir‐boosted protease inhibitor, such as atazanavir, is 150 mg every other day, higher dosages may be required to attain optimal rifabutin concentrations in patients receiving these drugs concomitantly.

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