Antibiotic therapy for purulent skin and soft tissue infection

What it is

Purulent means full of pus. Two purulent infections are set out in full here: the breast abscess that grows out of mastitis, and septic arthritis, where infection occurs within a joint. The joint may be a native joint or a joint replacement. Infection in a joint is an emergency, because it can quickly begin to destroy the joint and cause systemic illness.

Causes and risk

Mastitis starts when cracking of the skin around the nipple lets bacteria from the skin surface enter the breast duct, where they grow and attract inflammatory cells. Lactating mastitis is the more common form and is caused by staph. aureus, and milk stasis is one of the causes. Non-lactating mastitis goes with streptococcus: the central periareolar form is seen at a young mean age of 30 years and smoking is important in its aetiology, while the peripheral form is associated with diabetes, rheumatoid arthritis, steroid treatment and trauma. The third non-lactating form, granulomatous lobular mastitis, is seen in young multiparous women; its causes are idiopathic, TB and sarcoidosis, and it presents with a mass with or without erythema so that it mimics cancer, mostly unilateral, recurrent and troublesome. In the joint, Staphylococcus aureus is the most common causative organism, and the others are Neisseria gonorrhoea in sexually active individuals, Group A Streptococcus, Haemophilus influenza and Escherichia coli. The routes are contiguous spread from skin infection and cutaneous ulcers; direct inoculation through a previous intraarticular injection, a prosthetic joint or recent joint surgery; and hematogenous spread in diabetes mellitus, human immunodeficiency virus infection, immunosuppressive medication, intravenous drug abuse, osteoarthritis, another cause of sepsis, a late prosthetic joint, rheumatoid arthritis and sexual activity, that last one specifically for gonococcal arthritis. Age older than 80 years is set apart under other factors.