The perspective of the study was of the third-party payer incorporating only the direct costs of treatment, hospitalization, and diagnosis. The direct micro costing technique was used to determine the hospitalization expenditure per day of hospitalization, medications, diagnostic tests (blood count, urine cultures, blood cultures, uranalysis, CSF culture, PCR, PCL), diagnostic images (chest x-ray, renal ultrasound), medical and nursing procedures. Medical direct costs were valued at market prices, using as reference standard fees from Colombia´s Social Security manual. Generally, contracts between insurers and providers of health services is based on this national tariff manual [
14]. All information were evaluated by a group of experts (head of the pediatrics service, pediatric infectologist, head of purchases and supplies, and medical auditors of the service); and which also agreed on the range of lower and higher values for each cost. All costs were expressed in US dollars (Exchange rate 01/06/21, 1 US$ = COL $ 3800) [
14]. The cost of the Rochester scale included the cost of a blood count and a complete urine test with urine culture. The cost of procalcitonin and C-reactive protein included the direct costs of testing. The cost of hospitalization of false positive for SBI included the costs of medicines, diagnostic tests, and other costs described above during 3 days of hospitalization, period after which blood culture and urine culture readings are obtained with which hospital discharge is granted in patients with good clinical evolution and negative results in said cultures. The cost of hospitalization of a false negative included the costs of a first hospitalization for 3 days, such as those mentioned above for the case of a false positive, and the costs of a second hospitalization for the management of an SBI (cost of false positive + cost of true positive) [
8]; only including management costs in pediatric hospitalization without including derived from care in pediatric intensive care unit given the low rate of complications and mortality associated with SBI in infants with FSFS reported both locally and internationally [
9,
10]. Indirect costs (e.g., absenteeism costs, etc.) and direct non-medical costs (transportation, etc.) were not considered. Cost-effectiveness was evaluated at a willingness-to-pay (WTP) value of US$5180 [
15].