The diseases caused by S. aureus can be divided into two groups: (a) inflammatory and (b) toxin-mediated staphylococcal diseases.
These include the following conditions:
· Staphylococcal skin infections include impetigo, folliculitis, furuncles, carbuncles, paronychia, surgical wound infection, blepharitis, and postpartum breast infection.
· S. aureus is the most common cause of boils. The infection isacquired either by self-inoculation from a carrier site, such as the nose or through contact with another person harbor-ing the bacteria.
· Bacteremia and septicemia may occur from any localized lesion, especially wound infection or as a result of intrave-nous drug abuse.
· S. aureus is an important cause of acute bacterial endocardi-tis, of normal or prosthetic heart valves, which is associated with high mortality.
· S. aureus is the most common cause of osteomyelitis in chil-dren. The bacteria reach bone through blood stream or by direct implantation following trauma.
· S. aureus causes pneumonia in postoperative patients follow-ing viral respiratory infection, leading to empyema; it also leads to chronic sinusitis.
· S. aureus causes deep-seated abscesses in any organ afterbacteremia.
These include (a) staphylococcal food poisoning, (b) staphy-lococcal toxic shock syndrome, and (c) staphylococcal scalded skin syndrome.
Staphylococcal food poisoning: Staphylococcal food poison-ing is caused by enterotoxin. The enterotoxin is a preformed toxin, already present in the contaminated food before consumption. Milk and milk products and animal products like fish and meat kept at room temperature after cooking are mainly incriminated. When kept at room temperature, the contaminating staphylo-cocci multiply and produce toxin adequate enough (as little as 25 mg of toxin B can lead to illness) to cause food poisoning.
The toxin acts by stimulating the release of large amounts of interleukins IL-1 and IL-2. It is fairly heat resistant and so is not inactivated by brief cooking.
Often a food handler, who either is a carrier of S. aureus (nose, skin) or is suffering from staphylococcal skin infection, is the source of infection. The onset of symptoms is sudden, appearing within 2–6 hours of ingestion of food. It is a self-limiting condition characterized by nausea, vomiting, abdomi-nal cramps, and watery, nonbloody diarrhea.
Staphylococcal toxic shock syndrome: Staphylococcal toxicshock syndrome (STSS) is caused by TSST. The toxin is a supe-rantigen, which causes STSS by stimulating the release of large amounts of interleukins IL-1 and IL-2 in the body.
The STSS is an acute and potentially life-threatening con-dition similar to Gram-negative sepsis and septic shock. STSS is a multisystem disease characterized by fever, hypotension, myalgia, vomiting, diarrhea, mucosal hyperemia, and an ery-thematous rash followed by desquamation of the skin, particu-larly on palms and soles.
This condition was first documented in 1980 in the United States among the menstruating women who used highly absor-bent vaginal tampons; the vaginal swab from these women showed a heavy growth of S. aureus. This condition can also occur in other individuals, who have a local site of staphylococ-cal infection on skin or mucosa or on any other extragenital site.
Staphylococcal scalded skin syndrome: Staphylococcalscalded skin syndrome (SSSS) is caused by the exfoliative toxin, exfoliatin. The condition is seen commonly in infants and chil-dren. It is associated with extensive exfoliation of the skin, in which outer layer of the epidermis is separated from the under-lying tissue and is characterized by the appearance of extensive bullae. These bullae when ruptured may leave behind scalded, red, tender skin. The lesion typically starts periorificially or in skin folds. It usually resolves within 10 days’ time.
Pemphigus neonatorum and bullous impetigo are the milder forms, whereas Ritter’s disease in the newborn and toxic epidermal necrolysis in the older persons are the severe forms of the SSSS.
Complications of Staphylococcal Diseases
Complications of staphylococcal diseases include bacterial pneumonia, septicemia, arthritis, meningitis, etc. These com-plications are frequently seen in persons with extreme of age, debilitated persons, and immunosuppressed hosts.