Staphylococcal "Staph" Skin Infections: A detailed analysis

“Staph” is short for Staphylococcus, a type of bacteria. There are over 30 types, but the principal disease-causing bacteria of staph infections is known as Staphylococcus aureus (S. aureus). Studies show that about one in three people normally carry S. aureus in their nose, usually without any illness [1]. Two in 100 people carry methicillin-resistant S. aureus (MRSA), a type of staph bacteria that is resistant to several antibiotics [2].

Both community-associated and hospital-acquired infections with S. aureus have increased in the past 20 years, and the rise in incidence has been accompanied by a rise in antibiotic-resistant strains—in particular, methicillin-resistant S. aureus (MRSA) and, more recently, vancomycin-resistant strains [3]. In the general community, S. aureus and MRSA can cause serious infections of the skin, lungs, heart, bones, and joints.

Skin infections are the most common type of disease produced by S. aureus. Mortality due to staphylococcal infections varies widely. Untreated S. aureus bacteremia carries a mortality rate that exceeds 80% [3].

How Are Staph Infections Acquired?

Staph infections are highly contagious. They can be acquired through direct contact with an infected sore or wound.

They can also be spread by contact with commonly shared items (i.e. towels, soap, clothes) or with contaminated surfaces such as benches in saunas or hot tubs, or even by contact with shared athletic equipment.

Risk Factors for Staph Infection

Anyone can develop a Staph infection, although certain groups of people are at greater risk, including:

• Newborn infants
• Breastfeeding women
• Anyone with a chronic underlying health condition (e.g. diabetes, cancer, kidney failure, HIV/AIDS, lung disease)
• Anyone with skin damage — from conditions such as eczema to insect bites or minor trauma that opens the skin
• Post-surgical patients with surgical incisions
• Participants in contact sports
• Patients with weakened immune systems or who take immunosuppressant medications
• Intravenous drug users [4]

Soft-Tissue Infections Caused by Staph and Management

Skin abscesses

Skin abscesses are collections of pus within the dermis and deeper skin tissues.

A furuncle (or "boil") is an infection of the hair follicle in which purulent material (pus) extends through the dermis into the subcutaneous tissue, where a small abscess forms.

A carbuncle is a coalescence of several inflamed follicles into a single inflammatory mass with purulent drainage from multiple follicles. Small furuncles may heal on their own with good hygiene and wound care.

• Treatment: Incision and drainage is the primary treatment for simple furuncles and carbuncles. Bacterial gram stain and culture of pus from carbuncles and abscesses are recommended, but treatment without these studies is reasonable in typical cases. The decision to administer antibiotics directed against S. aureus as an adjunct to incision and drainage is made based upon presence or absence of systemic inflammatory response syndrome (SIRS).  An antibiotic active against MRSA is recommended for patients with carbuncles or abscesses who have failed initial antibiotic treatment or have markedly impaired host defenses or in patients with SIRS and hypotension (low blood pressure). Antibiotic treatment, if indicated, should be guided by the results of culture and sensitivity testing.

Empirical coverage of possible MRSA infections is warranted in the following settings:

• Severe or extensive disease (e.g. involving multiple sites of infection)
• Rapid progression in presence of associated cellulitis
• Signs and symptoms of systemic illness
• Associated comorbidities or immunosuppression
• Extremes of age
• Abscess in an area difficult to drain (e.g. face, hand, and genitalia)
• Lack of response to incision and drainage alone [8]

Impetigo

Impetigo, more commonly referred to as "school sores", is the most common bacterial infection in children. Impetigo occurs in two forms: bullous and nonbullous.

Nonbullous impetigo is the more common form, representing about 70% of impetigo cases [9]. It is more contagious than the bullous type [10].

It tends to affect skin on the face, trunk or extremities that has been disrupted by bites, cuts, abrasions, other trauma, or diseases such as chicken pox [11]. It occurs in adults and children but rarely in those under two years of age [12]. 

Lesions consist of fluid-filled blisters (bullae) that burst after a few days to leave a characteristic yellowish (honey-colored) crust. 

Regional lymphadenopathy is common and fever can occur in severe cases [13,14].

Non-bullous impetigo may resolve spontaneously without any treatment in 2-3 weeks [15]. Nonbullous impetigo is caused by Staphylococcus aureus, Streptococcus pyogenes, or a combination of both. Most infections begin as a streptococcal infection, but staphylococci replace the streptococci over time [16]. MRSA, which can be hospital- or community-acquired, is an increasingly common cause of impetigo [17]. This pathogen is observed more often with the nonbullous form of impetigo than the bullous form. Over the last decade, an increasing number of community-acquired MRSA and gentamicin-resistant S aureus strains have been identified in cases of impetigo [16].

Bullous impetigo occurs most commonly in intertriginous regions such as the diaper area, axillae and neck, although any cutaneous area can be affected, including palms and soles [18]. Bullous impetigo is most common among children aged two to five years [19-21]. Bullous impetigo may affect intact skin and is caused almost exclusively by S aureus.  S aureus produces a toxin that reduces cell-to-cell stickiness (adhesion), causing for the top layer of skin (epidermis), and lower layer of skin (dermis) to separate resulting in large areas of skin loss [16].

• Treatment: Treatment of impetigo typically involves local wound care along with antibiotic therapy. Gram stain and culture of the pus or exudates from skin lesions of impetigo are recommended to help identify whether S. aureus and/or a β-hemolytic Streptococcus is the cause, but treatment without these studies is reasonable in typical cases. Gentle cleansing, removal of the honey-colored crusts of nonbullous impetigo using antibacterial soap and a washcloth, and frequent application of wet dressings to areas affected by lesions are recommended. Good hygiene with antibacterial washes, such as chlorhexidine or sodium hypochloritebaths, may prevent the transmission of impetigo and prevent recurrences, but the efficacy of this has not been proven. Because S. aureus currently accounts for most cases of bullous impetigo, as well as for a substantial portion of nonbullous infections, antibiotic therapy with penicillinase-resistant penicillins or first-generation cephalosporins is preferred [12].   As community-acquired MRSA infection most commonly manifests as folliculitis or abscess, rather than impetigo, beta-lactam drugs remain an appropriate initial empiric choice. Systemic therapy is preferred for patients with numerous lesions or in outbreaks affecting several people (eg, athletic teams, childcare facilities) to help decrease transmission of infection. In patients with bullous impetigo who present to the emergency department with large areas of involvement resulting in denuded skin from ruptured bullae, management also includes intravenous fluid resuscitation.

Cellulitis

Cellulitis is a deep infection of the skin and the underlying tissues. If left unchecked, cellulitis can quickly lead to more dangerous infections of the blood (sepsis), bone (osteomyelitis) and heart (endocarditis) and in some cases tissue death (gangrene). Cellulitis is one of the most painful, quickly spreading and potentially deadly types of infections that can be caused by S. aureus or MRSA. A common bacterial infection of the skin, it can affect all ages.

Cellulitis infections are most common on the lower legs, face and arms, but they can occur anywhere on the body. Children often get this infection on their bottom [24]. Symptoms and signs are usually localised to the affected area, but patients can become generally unwell with fevers, chills and shakes (bacteraemia). Cultures are recommended in patients who are on chemotherapy for cancer, have low white blood cell counts, or who have a deficiency of their immune system, and for immersion injuries and animal bites.

• Treatment: Since routine cultures are not recommended, antibiotics are often chosen empirically based on the strongest available scientific evidence. 

Cellulitis without associated purulent drainage or abscess Streptococci continue to be the most likely pathogens in this setting.

Cellulitis with purulent drainage and/or abscess In cases of cellulitis with purulent drainage, abscess or both, MRSA is likely.             

Staphylococcal scalded skin syndrome

Scalded skin syndrome, also known as Ritter disease, is a relatively rare condition most commonly seen in infants and children under the age of five [25]. Staphylococcal scalded skin syndrome, also known as Ritter von Ritterschein disease (in newborns), Ritter disease, or staphylococcal epidermal necrolysis, encompasses a spectrum of superficial blistering skin disorders caused by the exfoliative toxins of some strains of S aureus. It is a syndrome of acute exfoliation of the skin typically following an erythematous cellulitis.

• Treatment: Patients need fluid rehydration, topical wound care similar to the care for thermal burns, and parenteral antibiotics to cover S aureus. Topical therapy with agents, such as fusidic acid and/or mupirocin, can be used as adjuncts to intravenous antibiotics, but they should not be used alone in true cases of staphylococcal scalded skin syndrome. Consideration must be given for the sharply increasing rates of community-acquired S aureus infection (CA-MRSA). Prompt treatment with parenteral anti-staphylococcal antibiotics is essential. Most staphylococcal infections implicated in staphylococcal scalded skin syndrome have penicillinases and are resistant to penicillin. 

Other Infections Are Caused by Staph

Staphylococcal pneumonia: Staphylococcal pneumonia predominantly affects people with underlying lung disease and can lead to abscess formation within the lungs.

Osteomyelitis: Osteomyelitis is an infection of the bones and is caused due to the S. aureus bacteria breaking into the body's tissues and entering the bloodstream through an open wound.

Staphylococcal sepsis: Staphylococcal sepsis is a leading cause of shock and circulatory collapse, leading to death, in people with severe burns over large areas of the body. When untreated, Staph aureus sepsis carries a mortality (death) rate of over 80%.

Staphylococcal food poisoning: Staphylococcal food poisoning is an illness of the bowels that causes nausea, vomiting, diarrhea, and dehydration. 

It is caused by eating foods contaminated with toxins produced by Staphylococcus aureus. Symptoms usually develop within one to six hours after eating contaminated food. The illness usually lasts for one to three days and resolves on its own. Patients with this illness are not contagious, since toxins are not transmitted from one person to another.

Septic arthritis: Decreased range of motion, warmth, erythema, and tenderness of the joint with constitutional symptoms and fever; however, these signs may be absent in infants (in whom the hip is the most commonly involved joint).

Endocarditis: Infective endocarditis is an infection of the inner lining of the heart. It often damages the heart valves which can lead to heart failure although other structures may also become involved.

Toxic shock syndrome: Toxic shock syndrome. Toxic shock syndrome is an illness caused by toxins secreted by Staph aureus bacteria growing under conditions in which there is little or no oxygen. Toxic shock syndrome is characterized by the sudden onset of high fever, vomiting, diarrhea, and muscle aches, followed by low blood pressure (hypotension), which can lead to shock and death. There may be a rash resembling sunburn, with peeling of skin. Toxic shock syndrome was originally described and still occurs especially in menstruating women using tampons.

References

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