Germ density

The Germ density on the hands describes the number of microorganisms (such as bacteria, viruses, and fungi) per defined area of skin. It is usually measured in colony-forming units per square centimeter (CFU/cm²) measured. In infection prevention, germ density is a key metric for assessing the risk of infection and the effectiveness of hygiene measures.

Germ density by skin region

The distribution of germ density varies greatly depending on skin region, moisture level, and individual hand hygiene.¹:

Microbiological classification

1. Resident skin flora (site flora)
This flora is part of the skin's natural protective barrier. It permanently colonizes the upper layers of the skin, sebaceous glands, and hair follicles.

• Germs: Mostly harmless germs (e.g. Staphylococcus epidermidis).
• Function: Protection against the colonization of disease-causing pathogens.
• Characteristic: The germ density of the resident flora remains relatively constant.

2. Transient skin flora (landing flora)
These germs temporarily get onto the hands through contact with the environment, patients, or contaminated surfaces.

• Germs: Frequently pathogenic (disease-causing) agents.
• Danger: They are a major cause of nosocomial (hospital-acquired) infections.
• Characteristic: The germ count fluctuates massively and must be eliminated through hygienic hand disinfection.

Relevant influencing factors

Several factors can cause the germ density on the hands to increase exponentially:

• Jewelry and watches: A warm, moist environment develops under rings and wristwatches. Studies show that the bacterial count there can be up to a hundred times higher. For this reason, wearing jewelry is prohibited in everyday medical settings.
• Skin condition: Healthy skin has a natural protective film. Cracked, dry, or damaged skin, on the other hand, offers ideal breeding grounds for germs, causing the germ density to increase drastically.
• Hand hygiene: Proper hand disinfection is the most effective means of reducing germ density.

Practical implications

In hospital hygiene, measuring germ density (e.g., through swab tests) serves as an indicator of the quality of hygiene measures.

The primary goal of hygienic hand disinfection is the reduction of germ density by at least 5 log levels. This corresponds to an elimination of the transient flora by 99,999 %. Only in this way can the transmission chain of pathogens be effectively interrupted.

Sources:

1. McGinley KJ, Larson EL, Leyden JJ. Composition and density of microflora in the subungual space of the hand. J Clin Microbiol. 1988;26(5):950–953. ↩︎