NEW YORK (Reuters Health) – Occult Staphylococcus aureus bacteremia is a “rare but important” issue in adult emergency department patients, one that deserves closer attention, a team of physicians from the National Taiwan University Hospital in Taipei note in a paper online March 19 in Clinical Infectious Diseases.
“It’s not an uncommon experience for an emergency physician to be informed that his or her patient has a positive blood culture report but was discharged before the result of blood culture,” Dr. Shey-Ying Chen, an author on the paper, told Reuters Health by email.
“Usually, most of these ED discharged bacteremia patients could be safely recalled for re-evaluation in the ED or outpatient department without complication. However, in rare occasions in our experience some of these occult bacteremia patients’ condition worsened or even ran a rapidly fatal course. It was these experiences that prompted us to design this study,” Dr. Chen said.
The study was a case-control design evaluating the impact of occult S. aureus bacteremia on patient outcomes. Between 2001 and 2010, bacteremia blood culture results were reported as positive for a total of 1256 adult patients after they were discharged from their ED. Of these, 759 patients had true occult bacteremia, including 65 patients with S. aureus bacteremia. Three of these patients were lost to follow-up, leaving 62 “case” patients with true occult S. aureus bacteremia.
The study team matched each case patient to two patients with S. aureus bacteremia who were directly admitted from the ED (control group I) and two occult bacteremia patients with bacterial infections other than S. aureus (control group II).
According to the researchers, there were no significant differences between the case group and control group I (S. aureus, directly admitted) with respect to organ failure, septic shock, proportion admitted to the ICU, length of ICU stay, and death at 30 days.
In other words, the occult S. aureus bacteremia patients did not have worse clinical outcomes than S. aureus bacteremia patients who were directly hospitalized at the time of their initial ED visit, the authors note in their report. “This implies occult bacteremia infections were either at an early stage of sepsis when patients first visited the ED or were endogenously benign in their clinical course,” they write.
However, compared with control group II (bacteremia not caused by S. aureus), the case group (occult S. aureus bacteremia) did have “significantly higher rates of hospital admission, organ failure, septic shock, ICU admission and 30-day mortality.” In multivariate regression modeling, S. aureus infection was an independent risk factor for death among patients with occult bacteremia, with an adjusted odds ratio of 7.7 (p=0.015).
“We sincerely hope our study could remind first-line physicians the importance of history taking and physical examination, rather than just laboratory tests, in the early diagnosis of many diseases. It is especially true in a busy emergency department like our hospital,” Dr. Chen said.
In their paper, the researchers point out that because S. aureus bacteremia is frequently associated with endovascular or deep-seated infection, “prudent evaluation of patients without an apparent infection focus is imperative for first-line clinicians before discharging febrile patients from EDs or out-patient clinics.”
Infective endocarditis is “the most important infection focus result in occult S. aureus bacteremia,” Dr. Chen commented, one that can cause sudden death or severe comorbidities.
“However, early diagnosis of infective endocarditis is difficult and requires careful history taking and comprehensive physical examination to find out any trivial but important physical signs suggesting of endocarditis,” Dr. Chen said.
The researchers also note in their report, that due to significant differences in demographic and clinical characteristics, bacteriology, and outcome, “occult bacteremia in adult patients is a distinct disease entity from occult bacteremia in pediatric patients.”
Clin Infect Dis 2012.