Ulceration may persist even when symptoms resolve. Drowsiness may persist for prolonged periods or remain constant. Barring major disturbances, it will persist indefinitely. Occasionally the disease may persist and result in a chronic infection. The contractions may persist for many weeks before gradually subsiding. In some cases, depressive symptoms persist for longer periods. This cough may often persist for weeks after an illness. However, it does rarely persist for months to years. Some cases, however, may persist several decades. However, many threats to their survival persist. The cough may persist for weeks without appropriate treatment. Similarly, symptoms often persist for one to several weeks after successful eradication of the mites. After stopping, cognitive problems may persist for six months or longer. In some people, though rarely, vertigo can persist for years. Nevertheless, the older systems do persist in many jurisdictions.