From the Guidelines
You should get blood cultures if you have a urine culture positive for Staphylococcus aureus, especially following a recent heart attack. S. aureus in urine is unusual and often indicates a more serious systemic infection rather than just a urinary tract infection. This finding is particularly concerning after a heart attack because S. aureus can cause endocarditis (infection of heart valves), which is more likely in patients with recent cardiac events. Blood cultures should be drawn before starting antibiotics if possible, typically two sets from different sites, as recommended by the American Heart Association 1.
While waiting for blood culture results, empiric antibiotic therapy may be initiated based on your doctor's recommendation, often including antibiotics effective against S. aureus such as vancomycin, daptomycin, or an anti-staphylococcal penicillin if the organism is methicillin-sensitive. The presence of S. aureus in your urine may represent either hematogenous spread (bacteria traveling through bloodstream) or ascending infection, and determining this distinction is crucial for proper treatment. According to the guidelines, it is reasonable to obtain 3 blood cultures by separate venipunctures on the first day, and if there is no growth by the second day of incubation, to obtain 2 or 3 more 1.
Some key points to consider:
- Blood cultures are essential for diagnosing infective endocarditis and guiding antibiotic therapy 1.
- The American Heart Association recommends blood cultures for patients with fever of unexplained origin and a pathological heart murmur, a history of heart disease, or previous endocarditis 1.
- In patients with acute IE who are severely ill and unstable, 3 separate venipunctures for blood cultures should be performed over a short period such as 1 to 2 hours and empirical antibiotic therapy initiated 1. Don't delay seeking medical attention as S. aureus infections can progress rapidly and require prompt intervention.
From the Research
Urine Culture Positives for Staphylococcus Aureus with Recent Heart Attack
- The presence of Staphylococcus aureus in urine cultures can have various implications, including contamination, colonization, urinary tract infection, or bacteraemic seeding from another site 2.
- Studies have shown that S. aureus bacteriuria can be associated with subsequent invasive infection, including bacteremia 3.
- In patients with S. aureus bacteremia, follow-up blood cultures are essential to detect ongoing bacteremia and guide treatment 4, 5.
- The decision to perform blood cultures in patients with urine culture positives for S. aureus and a recent heart attack should be based on individual clinical characteristics and risk factors.
- Factors such as urinary catheterization, urological abnormalities, and comorbidities may increase the risk of S. aureus bacteremia and warrant further investigation 2, 3.
Blood Culture Recommendations
- The study by 4 recommends taking 2 blood culture sets on days 2 and 4 after the start of therapy to detect ≥90% of persisting S. aureus bacteremia.
- Another study by 5 suggests that follow-up blood cultures should be performed in patients with a single S. aureus-positive blood culture to manage the infection properly and prevent relapse.
- However, the study by 2 does not support the routine taking of blood cultures or treatment of asymptomatic bacteriuria in well patients with S. aureus bacteriuria.
Molecular Detection of S. Aureus in Urine
- A recent study by 6 explored the use of molecular detection of S. aureus in urine and found that a rapid nucleic acid amplification test (NAAT) had a higher sensitivity than conventional culture in detecting S. aureus in patients with S. aureus bacteremia.
- The study suggests that NAAT from urine could potentially identify cases with increased risk for S. aureus bacteremia, but further research is needed to investigate its clinical benefit.