Patterns of bacteremia in pediatrics practice: factors affecting mortality rates

Risk factors for mortality resulting from bloodstream infections in a pediatric intensive care unit

BACKGROUND

Bloodstream infections (BSIs) are prevalent in the critical care setting and have high attributable morbidity and mortality. The purpose of this study was to identify factors that significantly contribute to immediate as well as eventual mortality in patients with bloodstream infections at a pediatric intensive care unit (PICU).

METHODS

Retrospective review of 2097 clinical records from admissions to our PICU in a 2-year period. Two separate case-control models were used. In the first model, eventual mortality (EM CASES) reflected those patients with eventual mortality, and EM CONTROLS were those who survived. In the second, infection-related mortality (IRM) cases were those with infection-related mortality, defined as death within 7 days of BSI, and IRM CONTROLS were survivors past 7 days. Logistic regression was used to adjust for differences for 3 categories: patient characteristics, microbiology and treatment variables.

RESULTS

We identified 74 separate episodes of bacteremia. Having an underlying malignancy or immunodeficiency was the only independently significant predictor of eventual mortality for BSI isolated within the PICU. Patients with infection-related mortality more likely had Gram-negative bacteremia and/or fungemia, were older and had inadequate initial empiric antibiotic treatment at the time BSI was diagnosed.

CONCLUSIONS

Targeted and aggressive early interventions should guide the empiric treatment of BSIs, whereas prolonged broad spectrum treatment should be minimized to avoid the emergence of resistant pathogen organisms.

Three-year survey of bacteremia and fungemia in a pediatric intensive care unit

BACKGROUND

Knowledge of the pattern of blood stream infection (BSI) in patients in intensive care units (ICUs) can help determine antibiotic prescribing policy and infection control procedures. However, there have been few pediatric-based studies.

METHODS

Surveillance of BSI in a pediatric ICU for 3 years, amounting to 131 episodes of significant bacteremia and fungemia.

RESULTS

The incidence of BSI was 39.0 per 1,000 admissions (10.6 per 1,000 bed days). Eighty-four (64.1%) episodes were ICU-acquired, and 27 (20.6%) were community-acquired. Gram-positive, Gram-negative and anaerobic bacteria accounted for 62.2, 30.8 and 1.4%, respectively, of the 143 microorganisms isolated, 5.6% were yeasts. Neisseria meningitidis was the most common species in community-acquired infections, and staphylococci predominated in hospital-acquired episodes. Eighty-seven percent of patients had significant underlying disease, including 60.3% with congenitally acquired conditions. Intravascular devices were the most common source of infection, accounting for 41.2% of all episodes. The crude mortality in children with BSI was 26.5%, compared with 8.1% in those without BSI.

CONCLUSIONS

The pattern of BSI in ICUs is partly determined by the type of patient treated. However, some observations are generally applicable, notably the increasing importance of antibiotic-resistant bacteria that are often of low virulence and device-associated. Our experience suggests that universal use of broad spectrum empiric antibiotics to cover these pathogens (which risks further promoting antibiotic resistance) may not improve patient outcome. Our study provides a basis for other pediatric ICUs to evaluate their rates and outcomes of BSI.

Comparison of the BacT/Alert pediatric blood culture system, Pedi-BacT, with conventional culture using the 20-milliliter Becton-Dickinson supplemented peptone broth tube

The performance of the Pedi-BacT system, the BacT/Alert (Organon Teknika Corp., Durham, N.C.) pediatric blood culture bottle, was compared with that of a conventional 20-ml supplemented peptone broth tube (Becton-Dickinson Corp., Cockeysville, Md.) (BD system) in matched aerobic cultures. The tubes of the BD system were visually examined daily for 7 days and were subcultured during the first 24 h of incubation. Pedi-BacT cultures were mechanically agitated and continuously monitored for growth by the instrument. Of the 6,628 compliant pairs, 331 (5.0%) were positive in both systems, 220 (3.3%) were positive in the Pedi-BacT system only, and 170 (2.6%) were positive in the BD system only. One (0.02%) false-negative culture and 15 (0.2%) false-positive cultures occurred with the Pedi-BacT system while 20 (0.3%) false-negative cultures and 35 (0.5%) false-positive cultures occurred with the BD system. Of 288 clinically significant organisms detected in matched pairs from which a single isolate was recovered, 176 (61%) were recovered from both systems, 83 (29%) were recovered from the Pedi-BacT system only (P < 0.0001), and 29 (10%) were recovered from the BD system only. Members of the family Enterobacteriaceae (P < 0.01), miscellaneous nonfermenters (P < 0.05), and Candida spp. (P < 0.01) were isolated more frequently in the Pedi-BacT system than in the BD system. No significant difference in recovery of other organisms was found between the systems. The average time to detection for the Pedi-BacT system ranged from 11.5 h for streptococci to 29.7 h for enterococci, while that for the BD system ranged from 20.3 h for streptococci to 66.4 h for some nonfermenters. The BacT/Alert system is a reliable, labor-saving alternative to conventional blood culture methods.

Clinical implications of positive blood cultures

Positive blood cultures can be classified according to their veracity (true-positive or false-positive culture), clinical severity (inconsequential or life threatening), place of origin (community acquired or nosocomial), source (primary or secondary), duration (transient, intermittent, or continuous), pattern of occurrence (single episode, persistent, or recurrent), or intensity (high or low grade). In general, however, positive blood cultures identify a patient population at high risk of death. In my studies, patients with positive blood cultures were 12 times more likely to die during hospitalization than patients without positive blood cultures. Many bacteremias and fungemias occur in complicated clinical settings, and it appears that only about one-half of the deaths among affected patients are due directly to infection. Hence, it is appropriate to speak of "crude mortality" and "attributable mortality." Among hospitalized patients, recent trends include rising incidences of Staphylococcus aureus and coagulase-negative staphylococcal and enterococcal bacteremias and a dramatic increase in the incidence of fungemias. The diagnostic and therapeutic implications of blood cultures positive for specific microorganisms continue to evolve and are the subject of a large and growing medical literature.