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Daily blood cultures during febrile illness are standard of care in many centers for post allogeneic hematopoietic cell transplant patients (alloHCT). The clinical significance of obtaining daily blood cultures for febrile illness has not been examined to our knowledge in the literature. Daily blood cultures are associated with iatrogenic blood loss and central line access. We report the incidence rate of bloodstream bacterial infections (BBSI) after four consecutive negative blood cultures between 2000-2013. Other testing modalities for occult infection including CT scan, viral PCR, and fungal cultures were also examined.
Methods
A retrospective chart review between 2000-2013 was conducted. Included were alloHCT patients with febrile illness (defined as greater than four negative consecutive blood cultures). The descriptive statistics was calculated and Fisher’s exact test was used for comparison among rates.
Results
Between 2000-2013, 158 cases in 83 patients were identified who met our criteria (mean age 10.6 years). Indication for alloHCT: malignant 62 (74.7%), non-malignant 21 (25.3%); conditioning regimen: myeloablative= 52 (62.7%) reduced toxicity= 10 (12.1%), reduced intensity= 21 (25.3%). Incidence of neutrophil engraftment by day +30 was 67.5%, and incidence of aGVHD was 54.2%.
Of those patients with febrile illness, 12% had BBSIs after 4 consecutive negative cultures. Mean time to developing BBSI was 10.6 (+/- 4.19) days. The most common BBSI was Gram positive cocci (GPC) [89%]. Of these infections, 28% grew staphylococcus epidermidis. Gram negative rods (GNR) only compromised 11% of BBSIs found. A significant risk factor for BBSI was length of febrile illness greater than 7 days (p=0.016).
The most obtained modality for identifying other sources of infection were CT scans and viral studies (both culture and PCR) [61.2% and 61.4%, respectively]. The rate of positive results for these tests was 29.1% and 10.9%, respectively. Other tests utilized to find occult infection included fungal cultures (36.1%) and bronchoalveolar lavage (BAL) (15.3%). The rate of positivity for these tests was 0.63% and 4.4% respectively.
Discussion
Twelve percent of patients developed BBSI after 4 sequential days of negative blood cultures, the majority occurring >7 days of febrile illness. Of those infections, the majority were GPCs possible secondary to indwelling catheters colonization. Probability of finding a true BBSI after 4 negative blood cultures is very low. Of the different modalities used to search for occult infection, CT scans have the highest yield in comparison to viral, fungal or BAL studies, suggesting that obtaining CT scans earlier in fever may be beneficial. Utility of obtaining daily blood cultures in febrile alloHCT patients should be prospectively studied.