The University of Arizona Learn About Germs


UA College of Public Health






How Germs are Spread

Did you know?    Some bacteria can grow and divide every 20 minutes. This means that in one day one germ can grow to become 8 million germs.

The most common illness spread from swimming pool uople, animals, the air we breathe, the food we eat, and even from surfaces we touch. Scientists analyze this movement of germs in what is termed the “chain of infection”. The germ is the first link in the chain. This “agent “ may be a bacteria, fungi, virus or parasite and is found at some source. This “reservoir”, as it is called, could be a person, animal or plant that is that is already the host to the germ. The reservoir can also be a body of water, food, or even an inanimate object that transfers the agent to a new host. In this way, the germ can multiply in a new host organism and continue to spread.
Germs from other People
The most common way of becoming infected with a germ is by catching it from another person who is already infected. Studying a germ’s movement from one person or population to another is called epidemiology (from the Greek words “epi” meaning “on” and “demos” meaning “people”) Examples of germs we catch from others include the common cold or flu, chicken pox and strep throat. The mode of infection can be from direct contact, airborne transmission, or indirect contact from surfaces.
Direct Contact

Did you know?   In a recent observational survey in 5 cities, 77% of people washed their hands after using the public rest room. Men washed their hands 66% of the time. Women were cleaner, washing their hands 88% of the time.

In direct contact the contagious germs from one person are passed along to the next person. Transmission can be from touching another person, such as a in a handshake. Although the he skin is home to many organisms, mostly bacteria, the majority are benign. Staphylococci and streptococci are two common bacteria found on the skin that can cause infection. Some fungi also live on the skin and can be spread by direct contact, the most common being athlete’s foot.
The mucous membranes in the mouth contain many germs and can cause such diseases as pneumonia, ear infections, strep throat, and cold sores (herpes virus). These germs can be transferred to the hands from coughing and sneezing, and then, in turn, be passed along to other individuals by skin contact. Direct contact from kissing can also spread germs from the mucous membranes. The germs in the mouth can also be transferred to other individuals in droplet form. This mode of transmission is discussed in the following section.
In the more private areas of the body, gastrointestinal bacteria live on the skin. Unwashed hands after using the bathroom can cause the spread of germs such as the bacteria Esherichia coli. In persons suffering from gastroenteritis, unwashed hands can spread other bacterial organisms such as Salmonella and, in turn, spread these diseases to other individuals.
Direct contact with germs can also be spread from body fluids including blood. Exposure to bodily fluids can arise from some sexual practices, drug abuse involving needles, spilled blood, and blood transfusions. Note that all blood donations in the United States are screened for many infectious diseases including the bacterium causing syphilis, HIV virus , hepatitis B, and hepatitis C virus to name a few.
A pregnant woman may also pass on infectious diseases to her unborn baby. Germs can pass through the placenta such as in the case of the AIDS virus. Infections of the skin such as streptococcus can be passed along by contact during delivery. Although breastfeeding provides newborns with many benefits, woman to known to have certain viruses such as HIV have the potential to transfer infection to their babies from breast milk.

Droplet Transmission

Did you know?   When you sneeze germs can travel at 80 miles per hour.

Droplets are mucus secretions that are emitted into the air by coughing or sneezing. When a sick person emits droplets into the surrounding area they have the potential to infect others close by. These droplets are too heavy to stay suspended in the air for a long period of time and as a result they can only travel up to 3 feet. If a droplet comes in contact with the facial area of an individual they too may become infected with the germ. Droplets contain germs that are generally more contagious than those spread by direct contact and s are significant in the spread of bacteria such as pneumonia, ear infections, step throat, and meningitis. Most of the respiratory infections are also spread by droplets. Fungi, parasites and insects, as well as skin contact bacteria are not spread in droplet form.
Certain germs can travel in the air for greater than 3 feet. This type of germ spread is called airborne transmission. Airborne germs spread by attaching to droplets of moisture in the air or to dust particles. In this way they can travel very long distances where they can be inhaled by other people. While there are not a large number of germs that can spread in this way, they can be very infectious. Examples of these types of germs include the bacterium that causes tuberculosis, spores of the anthrax bacterium, and the virus that causes measles.
Indirect Contact

Did you know?   Some viruses and bacteria can live 2 hours or even longer on surfaces like cafeteria tables, door knobs and desks. In one study, Rhinovirus was recovered from surfaces in a hotel room up to 24 hours after being touched with guests infected with the virus.

Indirect contact involves the passive involvement of an intermediate object such as a door knob. When a person with a germ touches the doorknob, germs are left behind. A person who follows may pick up the germs from touching the door knob. Free living germs like bacteria and fungi can survive on inanimate objects longer than viruses. Moisture aids in germ survival. Rhinoviruses (cold) and stomach flu can be spread in this manner.
Animals and Birds
Did you Know: Approximately 3 % of American households have reptiles (lizards, snakes, turtles) as pets. The CDC estimates that each year 70,000 people in the US develop salmonella infection from pet reptiles. Children under 5 years old and people with weak immune systems should avoid contact with reptiles.
Infection with animals can be by either direct contact of a person with the animal such as in a dog bite, or contact with animal feces. Infection can also be from indirect contact from a surface that has been previously contaminated by an animal.
People may also contract diseases through a vector organism. In epidemiology a vector is an organism that does not cause the disease itself, but spreads infection by introducing germs from one host to another. The mosquito is a classic example of a vector organism, spreading such diseases as malaria and the West Nile virus.
Many germs are species specific, meaning they can only infect one species. However, other germs have the ability to cross species. In general it is the bacteria and parasites that are spread by animals. Viruses are mostly spread through a vector or intermediate host.
Ingestion of Food and Drinking Water

Did you know?    Poor personal hygiene contributes to approximately 50% of all food borne illness outbreaks.

Ingestion of contaminated food or drinking water is a common cause of disease. In this method germs can be transmitted to many individuals through a single source. E. coli is a bacterium present in many uncooked foods and if the food is not cooked or handled properly may cause the disease commonly called food poisoning. Municipal drinking water goes through a purification process to remove harmful organisms before it gets to the consumer. However, water from private wells may have contamination from the surrounding septic systems or other waste sources, with the potential to cause human illness when consumed.

Did you know?   The average person breathes about six liters of air every minute.

Airborne transmission from environmental sources such as the soil can also cause infections. Fungi that reside in the soil can release spores that are carried by the wind and are in turn inhaled by susceptible people. Exposure can result in skin and lung infections or flu-like symptoms. Windy conditions or disturbance of the soil during construction can increase this mode of transmission.
Recreational Water

Did you know?    The most common illness spread from swimming pool use is diarrhea. On average, people have about 0.14 grams of feces on their bottoms. When rinsed off during pool use, this can contaminate recreational water.

Recreational waters include bodies of water such as lakes and rivers, as well as pools, spas and the increasing number of public water features such as wave pools and water slides. Lakes and other natural water sources can become contaminated with germs from animal or human waste and sewage. This can cause a variety of symptoms such as gastrointestinal, skin, ear, respiratory, eye and wound infections.
According to the CDC, outbreaks of diarrhea illness have been increasing from recreational waters and Cryptosporidium is the leading cause of documented recreational water illness (RWI). When Cryptosporidium or other germs like Giardia or E. coli are released into the water during a bowel movement of an infected human or other animal, accidental swallowing of the contaminated water by another individual can cause disease. Disinfectants such as chlorine or special filtration systems can kill germs but some parasites such as Crytosporidium are particularly resistant to disinfectants. Natural water sources such as lakes and streams are not chlorinated.