Where S. aureus Lives?

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, 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 refrigerator (contamination from infected food worker);
  • athletic equipment, toys, workout surfaces;
  • air, water, soil, dust (less important sources).

Staph Reservoir

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

How is Staph Infection Spread

Staph may spread from one skin location to another (auto-infection), e.g. by picking the nose followed by scratching the skin, or by clothes. Person to person spread is possible via skin-on-skin contact, or with sharing toys, towels, sport equipment, public showers, sauna, or swimming pools. 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 with 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 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 heat-stable.

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;
  • sportsmen;
  • 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). 

What is Staphylococcus aureus?
Lab tests for staph
Folliculitis pictures

References:

  1. MRSA IN PIGS
    http://www.thepigsite.com/swinenews/16316/canadian-researchers-find-drugresistant-staph-in-pigs-and-farmers  
  2. HUMAN - ANIMAL - HUMAN SPREAD OF S. AUREUS
    http://www.cdc.gov/ncidod/EID/vol10no12/04-0387.htm 
  3. DOG BITE CAUSED STAPH ENDOCARDITIS
    http://www.medscape.com/viewarticle/452848_1
  4. STAPH MASTITIS IN COWS
    http://jerseyjournal.usjersey.com/Article%20Archive/Management/staphaureus.htm
  5. INCUBATION PERIOD OF S. AUREUS
    http://www.cinetwork.com/otero/mrsa.html  INF.
  6. STAPH FOOD POISONING INCUBATION PERIOD
    http://www.drgreene.com/21_1193.html  
  7. MORBIDITY AND MORTALITY FROM S. AUREUS in UNITED STATES
    http://www.cdc.gov/ncidod/dhqp/ar_mrsa_surveillanceFS.html