Staphylococcus aureus is not classified as a Sexually Transmitted Disease (STD). While it is a bacterium that can be passed between individuals through close physical contact, its primary means of transmission do not align with the criteria defining an STD. This common bacterium lives harmlessly on the skin or in the nose for most people. It becomes an opportunistic pathogen when conditions allow, leading to infections typically spread through non-sexual contact.
Classification of Staphylococcus Aureus
Staphylococcus aureus is a Gram-positive bacterium, meaning it retains the crystal violet stain used in a lab procedure. This spherical-shaped microbe is often found clustered together. It is considered a commensal bacterium, meaning it typically lives on a host without causing harm. An estimated 20% to 30% of the human population carry it on their skin or in their nasal passages at any given time.
A pathogen is designated as an STD if its primary and predominant route of transmission is through sexual activity, including vaginal, anal, or oral sex. STDs are typically spread through bodily fluids or contact with lesions on the genital area. S. aureus does not meet this primary criterion because its spread is overwhelmingly incidental, occurring through general skin-to-skin contact rather than being fundamentally dependent on sexual fluids or mucosa-to-mucosa contact for transmission.
Common Routes of Transmission
The most frequent way S. aureus spreads is through simple, direct skin-to-skin contact, which is common in many daily activities, not just sexual encounters. This kind of transmission occurs easily in crowded environments, between family members in a household, or among athletes sharing equipment. Since many people are asymptomatic carriers, they can unknowingly spread the bacteria just by touching surfaces or other individuals.
Transmission also happens readily through contaminated objects, known as fomites, because S. aureus can survive for extended periods outside the human body. Examples of these contaminated items include shared towels, bedding, athletic gear, and door handles. Healthcare-associated infections (HAIs) are another route, often transmitted in medical settings, particularly to patients with compromised immune systems or those with surgical wounds. The bacteria can also be transferred from the nose to other parts of the body by the hands of a colonized person.
Infections Caused by Staphylococcus Aureus
While colonization is often harmless, the bacterium becomes an opportunistic pathogen when it enters the body through a break in the skin barrier. S. aureus is the most common cause of skin and soft-tissue infections, which often manifest as localized, pus-filled lesions. These milder infections include folliculitis (infection of the hair follicle), impetigo (blisters that crust over), and abscesses (boils or furuncles).
A public health concern is the emergence of Methicillin-resistant Staphylococcus aureus (MRSA), a strain resistant to many common antibiotics. MRSA infections can be acquired in healthcare settings (HA-MRSA) or in the general community (CA-MRSA), and they are more challenging to treat. Beyond skin infections, S. aureus can cause severe, life-threatening systemic diseases if it enters the bloodstream. These include:
- Bacteremia (blood infection leading to sepsis).
- Endocarditis (infection of the heart valves).
- Osteomyelitis (infection of the bone).
- Conditions caused by powerful toxins, such as toxic shock syndrome or severe food poisoning.
Sexual Contact and Bacterial Spread
Although S. aureus is not an STD, sexual activity involves the kind of close physical contact that facilitates its transmission. The exchange of bacteria during sex is considered incidental spread, similar to sharing a bed or a towel, rather than a primary mode of transmission. Close skin-to-skin contact, especially when coupled with friction or the presence of minor cuts or abrasions, can allow the bacteria to move from one partner’s colonized area to the other.
If one partner is colonized with a virulent or drug-resistant strain, such as MRSA, it is possible for the bacteria to be shared during intimate moments. The genital area can be a site for S. aureus colonization, and the warmth and moisture in these regions can increase the susceptibility to infection. Transmission during sex is a direct consequence of the physical proximity inherent in the activity, not a reliance on sexual fluids for survival. Practicing good personal hygiene and keeping any wounds covered can help reduce the risk of this incidental bacterial exchange.