The human body hosts a vast community of microorganisms, many of which live on our skin and inside our bodies without causing harm. This peaceful coexistence is known as colonization. One of the most common bacterial residents is Staphylococcus, or staph. While staph is a normal inhabitant, its presence can shift from harmless to harmful under certain conditions.
What is Staph Colonization?
Staph colonization is the presence of Staphylococcus bacteria, most often Staphylococcus aureus, on or in the body without causing illness. When a person is colonized, the bacteria live on the skin or in the nasal passages without any symptoms like pain, fever, or pus. A colonized person feels perfectly healthy.
Colonizing bacteria include different strains distinguished by their antibiotic susceptibility. One type is Methicillin-susceptible Staphylococcus aureus (MSSA). Another is Methicillin-resistant Staphylococcus aureus (MRSA), which is resistant to several antibiotics. Both strains can colonize individuals without causing immediate problems.
Where Staph Bacteria Reside and How Common It Is
Staphylococcus aureus has preferred habitats on the human body. The primary reservoir is the anterior nares, the area just inside the nostrils, from which bacteria can spread to other skin sites. Common habitats also include moist skin areas like the armpits, groin, and behind the knees. Less often, staph is found in the throat or gastrointestinal tract.
Staph colonization is common, with about 30% of people being persistent carriers of S. aureus in their noses. Another portion of the population carries the bacteria intermittently.
When Colonization Becomes an Infection
The transition from colonization to active infection occurs when bacteria bypass the body’s defenses. A primary trigger is a break in the skin from cuts, surgical incisions, scrapes, or an intravenous catheter. These openings can serve as a gateway for staph to enter deeper tissues or the bloodstream, where they multiply and cause infection.
A person’s immune status also plays a part. A weakened immune system makes a person more susceptible to infection from their own colonizing staph. When the body’s ability to fight invaders is compromised, the bacteria can gain the upper hand.
If the bacteria become invasive, they can cause skin infections like boils, cellulitis, or abscesses. If staph enters the bloodstream, a condition called bacteremia can occur. From there, the bacteria can travel to other parts of the body, potentially causing pneumonia, bone infections, or heart valve infections (endocarditis).
Who is at Risk and How Staph Spreads
Several factors increase the risk of staph colonization and spread. The bacteria are transmitted through direct person-to-person contact or by touching contaminated objects like doorknobs and gym equipment. Introducing the bacteria to the nose, mouth, or an open wound can lead to colonization.
Risk factors for acquiring staph include:
- Frequent exposure to healthcare settings like hospitals
- Living in crowded conditions
- Participating in contact sports
- Sharing personal items such as towels or razors
Individuals with certain pre-existing conditions are more vulnerable to both colonization and infection. This includes people with skin conditions like eczema, which cause breaks in the skin. Those with diabetes or a compromised immune system also face an elevated risk.
Addressing Staph Colonization
Routine screening for staph colonization is not standard for the general public. However, healthcare providers may test for it in specific situations, such as before a major surgery like a cardiac or orthopedic procedure. Identifying and treating colonization beforehand can reduce the risk of a surgical site infection. Testing may also be used to investigate an outbreak or for people with recurrent skin infections.
A healthy, colonized individual with no symptoms or high-risk factors does not require treatment. When reducing the bacterial load is necessary, a process called decolonization may be recommended. This is a proactive measure to prevent future infections, not a treatment for an active one.
Decolonization involves using an antibiotic ointment like mupirocin inside the nostrils and washing with an antiseptic body wash containing chlorhexidine. These steps help lower the amount of staph bacteria on the body.