The spleen is involved in maintaining immunity and plays an important role in the elimination of encapsulated bacteria and parasites. Patients who undergo splenectomy in conjunction with complete CRS for peritoneal malignancy are at risk of overwhelming post-splenectomy infections post-operatively. These patients are therefore administered vaccinations to lower the risk of infections but as they do not completely eliminate the risk, patients are also prescribed prophylactic antibiotics without clear evidence that they are useful in preventing OPSI. The use of prophylactic antibiotics is not without risk with potential short and long-term risks including resistance, interaction with other medication, clostridium difficile infections, fungal infections, other changes to the microbiome and cost. This study will investigate the incidence of OPSI post splenectomy and assess compliance with prophylactic antibiotics. This is an observational study where consented patients will be telephoned at fixed time points which are 1,6,12 weekly and 6 monthly for a period of five years post-operatively. As part of routine care patients will be telephoned by the clinical nurse specialist at weeks 1,6 and 12. In addition to this the research nurse will telephone the patient 6 monthly for a period of 5 years and complete a questionnaire. The research nurse will complete the questionnaire during each telephone call and this should not take more than 20 minutes. At the start of the telephone call, consent will be confirmed each time and the research nurse will check that the patient is still happy to participate before going ahead.