252. Increased incidence rates of positive blood cultures shortly after chemotherapy treatment initiation among individuals treated for solid malignant tumours

Background Cancer treatments suppress immune function and are associated with increased risk of infections, but the overall burden of serious infectious diseases in treated patients has not been clearly elucidated. Methods All patients treated for solid malignant tumours with curative intent radiotherapy (RT) and/or standard first line chemotherapy (C) at the Department of Oncology at Rigshospitalet between 01/1/2010 to 31/12/2016 were included. Patients were followed from treatment initiation to new cancer treatment, end of follow up or death whichever came first. We calculated incidence rates (IR) of positive blood culture (PBC) per 1000 person years follow up using Kaplan-Meier methods, and examined the proportion who died within 30 days of PBC. Results 13,275 individuals were included, 4,372 (33%), 6,349 (48%), and 2,554 (19%) treated with RT, C, or concomitant RT&C, respectively, contributing 21,493 person years follow-up. 6,930 (52%) were female, the median (IQR) age was 63 (53, 70), and the most common cancer diagnoses were breast (n = 2,593 [19%]), colorectal (n=1,422 [11%]), and stomach (n=1,246 [9%]). Overall, 564 individuals (4%) experienced 746 unique episodes of PBC, 188, 408, and 150 events in 143, 311 and 110 individuals treated with RT, C, and RT&C, of which 49 (26%), 104 (25%), 38 (25%) died within 30 days of PBC, respectively. IR of PBC significantly varied by treatment: 13.0 (95% confidence interval 11.1, 15.4), 43.9 (39.3, 49.0) and 32.0 (26.5, 38.5) per 1000 person-years follow up in the RT, C and RT&C groups, respectively (IR ratio = 3.36 (2.75, 4.10) and 2.45 (1.91, 3.14) for C and RT&C compared to RT, respectively) and time since treatment (figure). Escherichia coli (n=185, 25%), Staphylococcus aureus (n=102, 14%), Klebsiella pneumoniae (n=76, 10%), Enterococcus faecium (n=48, 6%), and Enterococcus faecalis (n= 37, 5%) were the top 5 microorganisms identified and did not vary by treatment category, p = 0.11, there were 31 (4%) cases of Candida. Incidence rate of positive blood culture (PBC) by time since treatment initiation (0–3 months, 0–6 months and >6 months) and the proportion who died within 30 days of PBC by treatment type among individuals treated for solid malignant tumours with radiotherapy [RT], chemotherapy [C] and concomitant RT&C at Department of Oncology at Rigshospitalet, University of Copenhagen between 01/1//2010 to 31/12/2016. Conclusion PBCs are seen more often within 3 – 6 months after C than after RT alone. PBCs are not common, but when they occur, mortality is high. More precise risk factors for PBC and prophylactic means and empiric treatments in selected high-risk patients should be investigated. Disclosures All Authors: No reported disclosures