Patients undergoing hematopoietic cell transplantation are at greatly increased risk for infection.  Infections that have been seen to occur with increased frequency or severity among these patients are considered opportunistic infections.  Several professional groups have outlined recommended behaviors to reduce potential exposure to such infections, such as hand washing, avoiding contact with individuals with respiratory, varicella, pneumocystis, and other known infections, following general food safety practices, using condoms during sexual intercourse, avoiding sharing cups and eating utensils, avoiding contact with soil or human fecal contaminants, good hand hygiene after contact with animals, and good oral hygiene and care.