Introduction Influenza can cause mild to severe illnesses and serious outcomes can result in hospitalisation or death. Clinical presentation and management of influenza cases in Saudi Arabia have been tackled especially during 2009 H1N1 pandemic, however, available data on influenza related hospital stay and determining factors in the country is limited. This study aims to assess factors that determine the length of stay (LOS) among hospitalised influenza confirmed cases in King Abdulaziz Medical City – western Saudi Arabia.

Methods A retrospective review of laboratory-confirmed influenza cases admitted to King Abdulaziz Medical City during the period from January to December 2016 was conducted. Identified variables included age, gender, influenza strains and associated comorbidities.

Results Among the 556 laboratory-confirmed influenza cases during the study period, 157 patients were admitted (28.2%). More than half (52.2%) of the admitted patients were females, 20.4% were ≤5 years old, 51.6% were >5–65 years old and 28.0% were >65 years old. Healthcare workers represented 3.2% of the admitted patients. Influenza A-non H1N1 represented 65.6% followed by influenza B (36.3%) and influenza A-H1N1 (10.8%). Some patients have more than one episode of influenza. Most patients (65.0%) were admitted for more than 2 days (41.4% for 2–5 days and 23.6% for more than 5 days). Length of stay was significantly longer among elderly patients (>65 years old) and patients with DM, cardiac, chronic respiratory, immune deficiency diseases and with increased number of co-morbidities, however, no statistical significant association was reported according to influenza strains.

Conclusion Significant number of patients were admitted because of influenza for duration more than 2 days. Length of stay was associated with chronic morbidities and old age. Enhancement of immunisation programs especially for high risk patients is essential for reducing burden of influenza on patients and healthcare system.