Blood Cultures in the Emergency Department Evaluation of Childhood Pneumonia

Samir S. Shah, MD, MSCE; Maria H. Dugan, BA; Louis M. Bell, MD; Robert W. Grundmeier, MD; Todd A. Florin, MD; Elizabeth M. Hines, BA; Joshua P. Metlay, MD, PhD

Disclosures

Pediatr Infect Dis J. 2011;30(6):475-479. 

In This Article

Methods

Study Design, Setting, and Participants

This case–control study was nested within the cohort of children followed up at 35 pediatric primary care practices affiliated with The Children's Hospital of Philadelphia (CHOP) Pediatric Research Consortium, an Agency for Healthcare Research and Quality (AHRQ)-funded practice-based research network. Children must have had at least 1 well-child visit in the 12 months before diagnosis of CAP to be considered within this cohort. The Pediatric Research Consortium sites span 3 states (Pennsylvania, Delaware, and New Jersey) including urban, suburban, and semirural locations. Patients from this cohort who were ≤18 years of age, evaluated in the CHOP ED between January 1, 2006 and December 31, 2007, and diagnosed with CAP (as defined by a physician-assigned International Classification of Diseases, ninth revision, discharge diagnosis code [481–486] for pneumonia) were eligible for inclusion. Patients were excluded if they required hospitalization ≤14 days before the diagnosis of pneumonia or had an immunocompromising or chronic medical condition predisposing them to severe or recurrent pneumonia (eg, primary or acquired immune deficiency, cystic fibrosis, active chemotherapy for malignancy, sickle cell disease).

Patients with CAP were classified into 3 mutually exclusive groups as follows: those with documented bacteremia (cases), those without bacteremia as documented by a negative or contaminated blood culture (control group 1), and those without a blood culture (control group 2). This study was reviewed and approved by the CHOP Committees for the Protection of Human Subjects.

Data Collection and Study Processes

The following data were abstracted: demographic information including age, race, gender, comorbidities, and vaccination status; clinical and laboratory data from the ED visit; blood culture results; and the presence or absence of pneumonia-associated complications. Among patients with positive blood cultures, the medical records were reviewed further to determine whether culture results led to a change in antibiotic management (eg, broadening or narrowing of therapy) or any additional diagnostic interventions (eg, additional blood cultures, other laboratory testing, radiologic imaging).

All chest radiographs were reviewed by an attending pediatric radiologist as part of routine clinical care. The formal dictated report was further reviewed independently by 2 investigators. Chest radiographs were classified by the presence or absence of any infiltrates (defined as alveolar infiltrates, air bronchograms, and perihilar opacities), bilateral infiltrates, and pleural effusions. Discrepancies in interpretation of the dictated report, which occurred in <1% of items, were resolved by consensus.

Blood cultures were performed at the discretion of the attending physician. Only blood cultures obtained in the ED were included for analysis. Blood cultures were collected by ED nurses, according to standard procedures, using sterile technique. Blood was inoculated into pediatric blood culture bottles (Pedi-Bac T; bioMerieux, Durham, NC) containing supplemented brain heart infusion broth with 0.02% sodium polyanethol sulfonate. Blood cultures are normally delivered to the laboratory within 1 hour of collection through a pneumatic tube system. All blood cultures are then processed in a microbial detection system (BacT/Alert; bioMerieux) which monitors carbon dioxide production within each bottle every 10 minutes, 24 hours per day. Bottles identified as positive were immediately removed by a technician to perform a gram stain and subculture.

Study Definitions

Bacteria defined as pathogenic included Streptococcus pneumoniae, Staphylococcus aureus, group A beta-hemolytic streptococci, and H. influenzae. Bacteria defined as contaminants included coagulase-negative Staphylococcus species, α-hemolytic streptococci, Micrococcus species, and Corynebacterium species. S. pneumoniae blood culture isolates were also defined as penicillin susceptible or nonsusceptible according to the minimal inhibitory concentration criteria set by the Clinical and Laboratory Standards Institute.[15] Blood cultures were considered negative if no growth was reported after 5 days. Time to positivity was defined as the interval between specimen collection and result availability.

Pneumonia-associated complications were defined as the presence of one or more of the following: complicated pneumonia, organ dysfunction, metastatic infection, and death. Complicated pneumonia was defined as at least one of the following: lung abscess, parapneumonic effusion/empyema, lung necrosis, or bronchopleural fistula. Organ dysfunction was defined as sepsis, respiratory failure, or dysfunction in cardiovascular, neurologic, hematologic, renal, or hepatic systems according to international consensus guidelines.[16] Metastatic infection was defined as at least one of the following: probable or definite endocarditis,[17,18] mastoiditis, meningitis, pyomyositis, osteomyelitis, or septic arthritis. Asthma was classified as intermittent, mild persistent, or moderate/severe persistent according to national guidelines.[19] Pneumococcal vaccination status was coded as complete (4 doses), partial (1–3 doses), absent (eligible based on age but none received), or not applicable (not eligible based on age).

Statistical Analysis

Continuous variables were described using median, mean, interquartile range, or range values and compared between cases and controls using the Wilcoxon rank sum test. Categorical variables were described using counts and frequencies and compared between cases and controls using the Fisher exact test. Binomial exact 95% confidence intervals (CI) were calculated to determine the precision of estimate of prevalence for bacteremia and contaminated blood cultures.

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