Finding significant pathogens in blood cultures in children: Should we set the timer to 36 hours?

Background: Knowledge of time to positivity (TTP) for blood cultures is useful to assess timing of discontinuation of empiric antimicrobials for suspected bacteremia with no focus. Methods: An audit of positive blood cultures from the Children's Hospital of Eastern Ontario (CHEO) from November 1, 2019, to October 31, 2020, was performed to determine TTP, defined as the start of incubation to a positive signal from automated incubators. Results: Three hundred seventy-six positive blood cultures were identified from 248 patients (average age: 6.27 [SD 6.24] years). Of these, 247 isolates were speciated; 90 (36.4%) were definitive/probable (DP) pathogens (median TTP 12.75 hours) and 157 (63.6%) possible/probable (PP) contaminants (median TTP 24.08 hours). At each time point, the adjusted rate of positive blood culture was significantly higher for DP pathogens compared to PP contaminants (hazard ratio [HR] 1.80 [95% CI 1.37, 2.36]) and for children ≤27 days old compared to the oldest age group (HR 1.94 [95% CI 1.19, 3.17]). By 36 hours, the proportion of positive cultures was significantly higher in the youngest age group (≤27 days) compared with the 3-11 years old age group (91.7% [95% CI 68.6%, 97.8%] versus 58.2% [95% CI 46.91%, 68.06%]). Conclusion: Across all ages, the TTP was significantly shorter for blood cultures with DP pathogens compared to those with PP contaminants (HR 1.80 [95% CI 1.37, 2.36]). In newborns, 90% of blood cultures were positive by 36 hours supporting this re-assessment time for empiric antimicrobials. TTP was longer in children ≥12 months, possibly related to other factors such as blood culture volume.

Historique: Il est utile de connaître le délai de positivité (DdP) des hémocultures pour évaluer le moment de mettre un terme aux antimicrobiens empiriques en cas de présomption de bactériémie sans source apparente. Méthodologie: Les chercheurs ont procédé à un audit des hémocultures positives du Centre hospitalier pour enfants de l'est de l'Ontario (CHEO) entre le 1er novembre 2019 et le 31 octobre 2020 pour déterminer le DdP, défini comme la période entre le début de l'incubation et le signal positif d'incubateurs automatisés. Résultats: Les chercheurs ont extrait 376 hémocultures positives provenant de 248 patients (d'un âge moyen de 6,27 ± 6,24 ans). De ce nombre, ils ont différencié 247 isolats, dont 90 (36,4 %) étaient des agents pathogènes confirmés ou probables (CP) (DdP médian de 12,75 heures) et 157 (63,6 %), des contaminants possibles ou probables (PP) (DdP médian de 24,08 heures). À chaque point temporel, le taux corrigé d'hémocultures positives était sensiblement plus élevé à l'égard des agents pathogènes CP que des contaminants PP (rapport de risque instantanés [RRI] : 1,80 [IC à 95 % 1,37,2,36]) et des nouveau-nés de 27 jours de vie ou moins que des enfants plus âgés (RRI 1,94 [IC à 95 % 1,19,3,17]). Au bout de 36 heures, la proportion de cultures positives était sensiblement plus élevée dans le groupe le plus jeune (27 jours de vie ou moins) que dans celui des enfants de trois à 11 ans, soit de 91,7 % (IC à 95 % 68,6 %, 97,8 %) par rapport à 58,2 % (IC à 95 % 46,91 %, 68,06 %). Conclusion: À tout âge, le DdP était sensiblement plus court, à l'égard des hémocultures contenant des agents pathogènes CP que des contaminants PP (RRI 1,80 [IC à 95 % 1,37,2,36]). Chez les nouveau-nés, 90 % des hémocultures sont positives au bout de 36 heures, ce qui appuie ce moment pour réévaluer la prise d'antimicrobiens empiriques. Le DdP était plus long chez les enfants âgés de plus de 12 mois, peut-être à cause d'autres facteurs comme le volume de l'hémoculture.

Use of Pulsed-Field Gel Electrophoresis to Determine the Source of Methicillin-Resistant Staphylococcus aureus Bacteremia.

Pulsed-field gel electrophoresis (PFGE) has historically been considered the gold standard in fingerprinting bacterial strains in epidemiological studies and outbreak investigations; little is known regarding its use in individual clinical cases. The current study detailed two clinical cases in which PFGE helped to determine the source of their methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. Patient A was found to have MRSA bacteremia after trauma in her pelvic area. MRSA was also found in her groin but not in her nostril and rectum. PFGE was performed that showed variable bands of her MRSA isolates from blood and groin, suggestive of different strains of MRSA. Her MRSA bacteremia was determined to be unrelated to her pelvic trauma. Patient B was found to have MRSA bacteremia after colonoscopy. MRSA was also found in his nostril and rectum. PFGE was performed that showed variable bands of his MRSA isolates from blood and rectum but identical bands of MRSA isolates from his blood and nostril. His MRSA bacteremia was determined to be unrelated to his colonoscopy procedure. The current study demonstrates the use of PFGE to rule out the source of bacteremia in individual clinical cases.

A Case Series of Diarrheal Diseases Associated with Yersinia frederiksenii.

To date, Yersinia pestis, Yersinia enterocolitica, and Yersinia pseudotuberculosis are the three Yersinia species generally agreed to be pathogenic in humans. However, there are a limited number of studies that suggest some of the "non-pathogenic" Yersinia species may also cause infections. For instance, Yersinia frederiksenii used to be known as an atypical Y. enterocolitica strain until rhamnose biochemical testing was found to distinguish between these two species in the 1980s. From our regional microbiology laboratory records of 18 hospitals in Eastern Ontario, Canada from 1 May 2018 to 1 May 2021, we identified two patients with Y. frederiksenii isolates in their stool cultures, along with their clinical presentation and antimicrobial management. Both patients presented with diarrhea, abdominal pain, and vomiting for 5 days before presentation to hospital. One patient received a 10-day course of sulfamethoxazole-trimethoprim; his Y. frederiksenii isolate was shown to be susceptible to amoxicillin-clavulanate, ceftriaxone, ciprofloxacin, and sulfamethoxazole-trimethoprim, but resistant to ampicillin. The other patient was sent home from the emergency department and did not require antimicrobials and additional medical attention. This case series illustrated that diarrheal disease could be associated with Y. frederiksenii; the need for antimicrobial treatment should be determined on a case-by-case basis.

A Case-Control Study on the Association between Salmonella Bacteriuria and Cystoscopy.

To date, there is only one published report of an outbreak of urinary tract infections by Salmonella species after cystoscopy. Disinfection procedures for cystoscope have come into question. The current study aimed to determine the odds of developing Salmonella bacteriuria after cystoscopy. A retrospective case-control study was conducted on all patients with Salmonella species in urine (case) and blood (control) from 2017 to 2019 in 16 hospitals in Eastern Ontario, Canada. Eight of the 11 patients had cystoscopy prior to Salmonella bacteriuria; three of the 74 patients had urological procedures prior to Salmonella bacteremia, but none of their procedures were cystoscopy. The odds ratio of urological procedures with Salmonella bacteriuria was 63.1 (95% CI 10.9 to 366.6; p < 0.0001). In the bacteriuria group, the most frequently identified isolates were Salmonella enteritidis (n = 8), followed by Salmonella oranienburg, and Salmonella heidelberg. Seven of the S. enteritidis isolates had identical susceptibilities (ampicillin-sensitive; sulfamethoxazole/trimethoprim-sensitive; ciprofloxacin intermediate). In the bacteremia group, the most frequently identified isolates were S. enteritidis (n = 22), followed by Salmonella typhi, S. heidelberg, S. oranienburg, and Salmonella typhimurium. The result suggested cystoscopy is a risk factor for Salmonella bacteriuria. Identification of Salmonella bacteriuria should prompt public health investigations of linkage between cystoscopy and Salmonella bacteriuria.

A Pregnant Patient With a Large Anterior Mediastinal Mass for Thymectomy Requiring One-Lung Anesthesia.

Anesthetic management for anterior mediastinal mass resection is often challenging. The main concern being that the tumor might, on reduction in muscle tone, cause circulatory and/or airway collapse. In the setting of pregnancy, the expected physiologic changes (eg, increased oxygen demand, decreased functional residual capacity, and aortocaval compression) may further increase the risks. The objective of this report is to present a challenging case of a pregnant woman undergoing an anterior mediastinal mass resection with the additional rare requirement for one-lung anesthesia, and to describe the perioperative considerations and the plan executed to ensure a successful outcome. A 30-year-old pregnant (23 weeks) patient with a large anterior mediastinal mass and evidence of significant cardiovascular and tracheobronchial compression presented for thymectomy requiring one-lung ventilation. Anesthesia consisted of preoperative preparation, thoughtful selection of vascular access sites, preservation of spontaneous ventilation until sternotomy was accomplished, use of bronchial blocker and readily reversible pharmacologic agents, availability of backup airway and oxygenation plans, standby high-frequency ventilation, and anticipation of postoperative respiratory difficulties. Surgical considerations included the possibility of extracorporeal membrane oxygenation and the need for lifting the thymoma to relieve the compression of the mediastinum. A methodical and multidisciplinary plan is described to mitigate the risk of cardiorespiratory collapse in the setting of anterior mediastinal mass resection. Backup measures in case of catastrophe, as well as careful consideration of the physiologic changes of pregnancy, must be taken into account.

First case report of infective endocarditis associated with Microbacterium maritypicum.

Microbacterium species are gram positive coryneforms generally considered as a contaminant when identified in gram stain of blood culture, especially when time-to-positivity is longer than 48 h. We encountered a case of infective endocarditis associated with Microbacterium maritypicum bacteremia, which became positive after 48 h of incubation in three out of four bottles. The antimicrobial management is controversial as vancomycin is generally assumed to cover most gram positive bacilli, but our susceptibility result demonstrated minimum inhibitory concentration of 4 µg/mL of vancomycin, indicating non-susceptibility. To the best of our knowledge, this is the first case report of infective endocarditis associated with Microbacterium maritypicum.