To describe the natural history of a condition or disease. To describe the natural history of a condition or disease. To determine effectiveness or cost effectiveness of treatments/services and/or health care products. To measure or monitor safety and harm. To measure quality of care.
According to the NMSS, attacks or flare-ups of symptoms only qualify as exacerbations if: 1  they occur at least 30 days from an earlier flare-up. 2  symptoms last for 24 hours or longer.
Viral hives can come and go, within a few hours or days, and can last up to four weeks. However, there have been cases where viral hives have been seen for as long as 6 weeks, moving them over into the chronic hives category. Viral hives often itch like crazy and can cover more than a small area of the body.