SIOUX FALLS, S.D. (AP) — South Dakota’s largest hospital systems are warning that they are strained and pushing off medical care as the state’s hospitals fill with the highest number of people infected with COVID-19 since the beginning of 2021. Officials with Sanford Health, Avera Medical Group and the city of Sioux Falls are urging people to get vaccinated and take precautions against spreading the virus during holiday gatherings. The state is seeing its worse surge of the virus since last winter. One in every 351 people in the state tested positive for the virus in the past week, according to Johns Hopkins researchers.