Staph Epidemiology

Where Does S. aureus Live?

What is Staphylococcus aureus?
Lab tests for staph

S. aureus lives in:

  • Healthy people (S.aureus carriers): in the mucosa of the nose, less commonly in the throat, vagina, intestines and lungs; on the skin: mainly in the armpits, under the breasts and in the groin
  • Infected people: in skin lesions, the blood, stool, urine, respiratory mucosa, genitals, abscesses of internal organs
  • Animals: in pets (fur, skin, nares) and farm animals (cows udders, horses, poultry)
  • Contaminated food: milk (from infected cow), food prepared and kept outside a refrigerator for some hours (contamination from infected food worker)
  • Athletic equipment, toys, workout surfaces
  • Air, water, soil, dust (less important sources).

Staph Reservoir

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Primary reservoir for S.aureus (including MRSA) is a human. Staph is common in cows (mastitis), poultry, and pets (dogs, cats). In Canada, they have found MRSA in pigs (1).

How Is Staph Infection Spread

Staph may spread from one skin location to another (auto-infection), for example, by picking the nose followed by scratching the skin, or by clothes. Person to person spread is possible via skin-to-skin contact, or with sharing toys, towels, sport equipment, public showers, sauna or swimming pools. An infection may also be spread by healthy staph carriers, especially by health personnel. Staph may spread from human to dogs or other pets and then back to the human (2). S. aureus may be found on the skin, hair, nostrils or saliva of dogs. Severe staph endocarditis was reported after a minor dog bite (3). Infection by milking a cow having staph mastitis is possible (4). Staph food poisoning may occur after ingesting food contaminated with staphylococci, released from an infected food worker.

Entry points of staph infection are:

  • Skin: a hair follicle during minor shaving trauma or depilation, acne, eczema (psoriasis, atopic dermatitis), skin injury, burns, injection, piercing and tattoo punctures, vascular and urinary catheters, surgical wounds;
  • Respiratory tract: staphylococcal pneumonia may be a complication of influenza or aspiration.

Farm to Table Continuum of S. aureus

Staph can survive on domestic animals such as dogs, cats and horses, and can cause a bumble-foot in chickens and mastitis in cows. When bacteria enter the milk or meat, they multiply and release toxin. Food poisoning is possible even with cooked milk, ice-cream, or smoked meat, like salami, since S.aureus toxins are not destroyed by heat.

Who Is at Risk to Get Staph Infection?

These are:

  • People with weak immune system: young children, old people in nursing homes, diabetics, cancer or AIDS patients, and those on immunosuppressive therapy or dialysis
  • Hospitalized patients with surgical wounds, burns, trauma, feeding tubes, catheters, prosthetic joints or heart valves
  • Health personnel
  • Intravenous drug addicts
  • Breastfeeding mothers
  • Athletes
  • Soldiers, prisoners and others living in crowded communities
  • Farmers may get infected from cows mastitis

Incubation Period of S. aureus

Incubation period of S.aureus infection may vary a lot, but it is commonly between 4-10 days (5). Incubation period in staph food poisoning is 30 minutes to 8 hours (6).

Staph Infection Incidence and Mortality

In United States, in y. 2006, approximately 32% of population was colonized with S. aureus and 0.8% with MRSA. MRSA causes about 94.000 serious infections and about 19,000 deaths in US each year (7).

Related Articles:

References:

  1. MRSA in pigs  (thepigsite.com)
  2. Human – animal – human spread of S. aureus  (cdc.gov)
  3. Dog bite resulted in staoh endocarditis  (medscape.com)
  4. Staph mastitis in cows  (usjersey.com)
  5. Incubation period of S. aureus  (cinetwork.com)
  6. Staph food poisoning incubation period  (drgreene.com)
  7. Morbidity and mortality from S. aureus in United States  (cdc.gov)
About Jan Modric (249 Articles)
Health writer