Occult Staph aureus
Bacteremia Important in Adult ED Patients
News Author: Megan Brooks
CME Author: Désirée Lie, MD, MSEd
Clinical Context
According to the current study by Chen and colleagues, blood
culture is the standard test for the diagnosis of bacteremia, but blood culture
results are never immediately available for decisions about admission in the
emergency department (ED). Hence, patients may be inadvertently discharged from
the ED but who are subsequently found to have bacteremia. Discharging patients
with bacteremia from the ED has been recognized as an important clinical
problem. In pediatric patients, it is known as occult bacteremia because this
patient group may look healthy with no identifiable infectious focus before
blood culture diagnosis results. The consequence of undiagnosed bacteremia
among discharged ED patients is not well known.
This 2-part case-control study determines outcomes for ED
patients discharged with unrecognized bacteremia by comparing patients with Staphylococcus
aureus bacteremia vs those with bacteremia not caused by S aureus
for morbidity and mortality outcomes.
Study
Synopsis and Perspective
Occult Staphylococcus aureus bacteremia is a
"rare but important" issue in adult emergency department (ED)
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 intensive care unit (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. Published online March 19, 2012.
Occult Staphylococcus aureus
Bacteremia in Adult Emergency Department Patients: Rare but Important
1.
Chia-Ming Fu1,
2.
Wen-Pin Tseng1,
3.
Wen-Chu Chiang1,2,
4.
Mei-Shu Lai2,
5.
Wei-Chu Chie2,
6.
Hao-Chang Chou1,
7.
Po-Ren Hsueh3,
10.
Shyr-Chyr Chen1,
11.
Wen-Jone Chen1,
and
12.
Shey-Ying Chen1,2
+
Author Affiliations
1.
1Department of Emergency Medicine, National
Taiwan University Hospital
2.
2Institute of Epidemiology and Preventive
Medicine, College of Public Health, National Taiwan University
3.
3Department of Laboratory Medicine, National
Taiwan University Hospital, Taipei, Taiwan
1.
Correspondence:
Shey-Ying Chen, MD, Institute of Epidemiology and Preventive Medicine, College
of Public Health, and Department of Emergency Medicine, National Taiwan
University Hospital, College of Medicine, National Taiwan University, No. 7
Chung-Shan South Rd, Taipei, Taiwan (erdrcsy@ntu.edu.tw).
Abstract
Background. We sought to elaborate the epidemiology and outcomes of adult patients
with occult Staphylococcus
aureus bacteremia who were inadvertently discharged from the
emergency department (ED) before positive blood culture results were obtained.
Methods. Between
2001 and 2010, 759 true occult bacteremia cases were identified, including 65
patients with S.
aureus bacteremia. Sixty-two patients were enrolled (case group)
and analyzed using two 1:2 case-control strategies. Control group I patients
were selected from among 997 S.
aureus bacteremia patients directly admitted from the ED. Control
group II patients were selected from 694 ED patients with occult bacteremia
other than S.
aureus. Cox regression analyses were used to assess the independent
effect of occult S.
aureus bacteremia on patient mortality.
Results. There was
no significant difference between the case group and control group I with
respect to organ failure, septic shock, intensive care unit (ICU) admission
proportion, length of ICU stay, and 30-day mortality. However, compared with
control group II, the case group had significantly higher rates of hospital
admission, organ failure, septic shock, ICU admission, and 30-day mortality.
Age, endocarditis, and S.
aureus infection were independent predictors of mortality among
adult occult bacteremia patients.
Conclusions. Among patients with occult bacteremia, S.
aureus infections had significantly greater adverse impacts on a
variety of outcome variables than other bacterial infections. Because S. aureus
bacteremia is frequently associated with endovascular or deep-seated infection,
it is imperative that first-line clinicians perform prudent evaluations of
cases with nonapparent infection foci before discharging febrile patients from
EDs.
Received September 29, 2011.
Accepted February 2, 2012.
Study Highlights
- The investigators conducted this retrospective study at
a single 2500-bed university hospital with an average of 100,000 ED visits
annually. - Records of all adult patients seen between 2001 and
2010 with positive blood culture results were reviewed for bacteremia. - Included were patients 15 years and older seen in the
ED who had positive blood culture results reported after ED discharge. - A central microbiology laboratory was responsible for
all clinical specimens and testing of blood cultures. - Positive results were reported directly to attending
clinicians. - If a patient had been discharged from the ED, the ED
administrative office was notified, and a senior ED resident contacted the
patient by telephone. - If the patient refused admission, then follow-up
occurred in the outpatient setting. - If the patient had been admitted to another hospital,
then all results were forwarded to that hospital, and a follow-up
interview about the patient's outcome was conducted 1 month after the
blood culture test. - Bacteremia was diagnosed if 2 or more sets of blood
cultures grew pathogenic bacteria in a patient with compatible clinical
manifestations. - Patients with occult bacteremia were considered to have
positive blood culture results and who were discharged from the ED before
the results were available. - The researchers conducted 2 case-control studies.
- In the first comparison, patients with occult S
aureus bacteremia were compared vs patients with S aureus
bacteremia who were admitted from the ED. - In the second comparison, patients with occult S
aureus bacteremia were compared vs patients with bacteremia other than
S aureus. - 2 matched control patients were found for each case
patient, for each of the comparisons. - Primary outcome measures were hospitalization for the
infection and 30-day survival duration. - Secondary outcomes were rate of hospital admission, ICU
admission, organ failure, septic shock, and lengths of hospital and ICU
stay. - Variables examined included comorbidity, sepsis
severity, empiric antibiotic treatment, and demographics. - A total of 1256 patients with positive blood culture
results were identified for the period. - Of these 1256 patients, 759 had true bacteremia, of
which 65 had S aureus bacteremia. - There were 997 control patients for the first
comparison (S aureus, directly admitted) and 694 control patients
for the second comparison (bacteremia other than S aureus). - Escherichia coli infection
accounted for 36.8% of isolates. - 33.7% to 57% of patients with occult bacteremia did not
receive appropriate empiric antibiotics after the initial ED visit. - For the first comparison, patients with occult
bacteremia had a lower percentage with previous cardiovascular accident
history and of receiving empirical antibiotics at the first ED visit. - Outcomes did not differ between the 2 groups except for
hospitalization rate (77.4% for the patients with occult bacteremia vs
100% for the patients with bacteremia who were hospitalized). - For the second control comparison, the case group had
more cases of end-stage renal disease, central vascular catheter
placement, and higher comorbidity scores. - Compared with the control group who had bacteremia
without S aureus, the case group had a higher percentage of
hospital and ICU admissions, organ failure, septic shock, metastatic
infection foci, and 30-day mortality. - Case patients had significantly longer hospital stays
than control patients. - S aureus infection was an independent
predictor of mortality among patients with occult bacteremia (adjusted OR,
7.737; P = .015) and remained elevated even when comorbidity was
added into the final regression model. - The authors concluded that patients discharged from the
ED with occult S aureus bacteremia vs patients admitted from the ED
with S aureus bacteremia did not have higher mortality rates, but
discharged ED patients with occult S aureus bacteremia had higher
mortality rates than those with other types of bacteremia. - They concluded that clinicians in the ED should perform
prudent evaluations of patients suspected of bacteremia before discharge.
Clinical
Implications
- Patients discharged from the ED with occult S aureus
bacteremia have similar 30-day outcomes vs patients admitted from the ED
with occult bacteremia. - Patients discharged from the ED with occult S aureus
bacteremia have worse outcomes than patients with bacteremia from
sources other than S aureus bacteremia.
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