Impact of Blood Culture Positivity Time on Clinical Management of Pediatric ICU Patients

Sepsis accounts for high morbidity and mortality rates in ICU globally. Early recognition of sepsis with appropriate antimicrobial therapy is critical for the appropriate management of patients (1).

Blood culture (BC) is considered the gold standard for sepsis etiological diagnosis , with good sensitivity ,but suffering usually of delay or even failure to detect microorganisms in patients already treated with antimicrobials and failure to identify pathogens other than bacteria or yeast (2, 3).

Time-to-positivity (TTP) of blood cultures is defined as the time from the start of incubation to a positive signal. Knowledge of the distribution of blood culture TTP is of clinical benefit in the re-evaluation of patients with a clinical syndrome consistent with infection. A low probability of bacteremia when blood cultures have remained negative after 24 hours (4). Positive episodes with TTP more than or equal 24 h are commonly optimally treated infections, catheter-related infections, or infections caused by slowly growing microorganisms such as Candida or anaerobic Gram-negative bacteria. Growth of multidrug-resistant Gram-negative bacilli is exceptional beyond 24 h. In current clinical practice, bacteremia is considered unlikely if blood cultures have been negative for 48-72 hours (5, 6). Most blood culture bottles turn positive in less than 4 days, shortening the duration of incubation appears the most relevant solution in order to free additional capacity(4).

Various disinfectants, such as povidone iodine (PVI), alcohol preparations, and chlorhexidine gluconate ethanol (CHG-ALC), are used for disinfection prior to blood culture sampling. Contamination rates of cultured blood samples vary according to the disinfectant used, sampling site, definition of contamination, and skill level of individuals performing the venipuncture.(7, 8)

In this study, Investigators assessed the real life clinical impact on septic ICU patients based on time of blood culture positivity time.

Aim(s) of the Research :

1. Evaluate the impact of blood culture positivity time in real -life clinical practice (patient management and reduction of ICU stay, as well as decreases in 30-days mortality.)
2. Investigates the probability of blood culture positivity after 24 hours.
3. evaluate if there was diagnostic value of TTP
4. Identify if there is difference in the blood culture contamination rate between uses of various type of disinfectant.

Sample Size Calculation: 120 septic patient in pediatric intensive care unit

Study tools:

The following will be done to all patients:

Data collection:

Clinical data (were retrieved from the medical records) :

* age and weight
* Date and time of culture collection
* pre-existing medical conditions (concomitant disease).
* Clinical parameters at presentation. The most likely source of bacteremia
* if start empirical antibiotic treatment before collection or not and its type, duration (concomitant antimicrobial therapy)
* volume of blood drawn in the bottles
* outcome data. Including change of antibiotic treatment and time to switch to directed therapy, length of ICU stay and 30-day mortality.

Microbiological data (were retrieved from the database of the Department of Medical Microbiology.) :

* date and time of bottle loading ( to know transportation time)
* date and time in which growth was first reported
* TTP(time to positivity of blood culture)
* Pathogen detected by blood culture

Blood culture sampling :

* collecting blood samples as soon as possible after the onset of clinical symptoms, ideally prior the administering antimicrobial therapy.
* Disinfection using povidone-iodine, alcohol preparation, or chlorhexidine gluconate ethanol (CHG-ALC ), so that each type was used on 40 patients
* collect 2 sets of blood culture bottles. blood culture was obtained either at one time or over a brief time period (e.g. within 1 hour) from multiple venipuncture sites.
* Blood for culture must be collected and dispensed aseptically with great care to avoid contaminating the specimen and culture medium

Blood culture handling procedures and laboratory techniques:

* Rapid transportation to microbiology unit.
* Rapid bottle loading in bioMerieux BacT/Alert Virtuo where it was incubated for 5 days
* Direct Gram stain was performed for all positive blood culture bottles.
* Followed by subculture onto solid agar media, including blood agar, chocolate agar \& MacConkey agar and sabaroud agar (Diagnostic Media products(DMP). Then identification of microorganisms and antibiotic susceptibility by Vitek 2.
* Direct reporting method to the pediatric intensive care unit
* The presence of one of the following microorganisms in a single BC bottle or Blood Culture set was considered as contaminant: coagulase-negative staphylococci (CoNS), with the exception of S. lugdunensis, Propionibacterium spp., Bacillus spp. other than B. anthracis, Corynebacterium spp. (diphtheroids), Aerococcus-like organisms, Micrococcus spp., viridans group streptococci other than S. pneumoniae, and Neisseria spp. other than N. gonorrhoeae or N. meningitidis. These microorganisms were considered as significant when other BC bottles collected 48h before were positive with the same microorganism, after reviewing of clinical data.

Eligibility Criteria:
Inclusion Criteria:

* The population of our study were patients in ICU unit in pediatric hospital of Assuit University Hospitals, that presented with clinical symptoms which may lead to a suspicion of a bloodstream infection or sepsis which is:

  * Undetermined fever ( ≥ 38°C) or hypothermia ( ≤ 36°C).
  * Shock, chills, rigors
  * Severe local infections (meningitis, endocarditis, pneumonia, pyelonephritis, intra-abdominal suppuration etc.) Multiple episodes of bacteremia per patient were allowed if the antimicrobial therapy for the previous episode had been completed and clinical and microbiological cure had been achieved

Exclusion Criteria:

-blood culture bottles that were drawn in vacation days (because of no distinct control on transportation time, which affect TTP)