Disease Transmission

What is needed for a disease to spread

There must be an agent that can cause disease

An agent is something that can cause illness. An agent can be a bacteria, virus, fungus, spore or parasite.

The agent must have a place to live (host or reservoir)

Bacteria, viruses and other agents must have a place to live (reservoir). Many agents live and multiply in humans and can be transmitted from person to person. In these cases human beings are the host.

Other agents, such as rabies, live in animals. People get infected with the agent through contact with an animal. In the case of rabies, a person gets infected when they are bitten by a rabid dog or other animal. An agent that is spread from animals to people is called a zoonosis.

The agent must have the right environment to survive outside of its host.

Like other living things, agents that cause disease need the right conditions to survive. After an agent leaves its host, it must have a suitable environment. For example, the bacteria that cause tuberculosis can survive in sputum for weeks, but will be killed by sunlight within a few hours. The bacteria that cause a type of pneumonia called Legionnaire’s disease live and multiply in the moist cooling towers of a building’s air-handling system.

There must be a person who can catch the disease (susceptible host)

People are exposed to disease causing agents every day but do not always get sick. A person who can catch a particular disease is susceptible to that disease.

People do not catch all the diseases they are exposed to because the body has a way to fight off disease. The human body’s defense against diseases is the immune system. The immune system destroys agents when they enter a person’s body.

A person can also develop protection (immunity) from diseases. For example, a person can only get chicken pox once. After the first time, the immune system protects the person from getting the disease again. People also get immunity from shots (vaccinations). The polio vaccination is an example of a how people can get protection. In both of these cases, the person has acquired immunity.

An agent must be able to move from its host to others (transmission)

An agent must have a way to move from a host (person or animal) to someone who can catch the disease. The way a disease spreads is called the mode of transmission.

Communicable diseases are mainly spread in these ways:

• Airborne: through the air; 
  
  
• Bloodborne: infected blood or other body fluids contaminated with blood that come into contact with another person’s blood such as through a needlestick; 
  
  
• Contact: touching or other direct contact with bodily discharges, secretions or waste, an open wound, bandage, soiled objects or infected surface; 
  
  
• Fecal-oral: swallowing food that has been contaminated by human or animal waste. Putting your hands in your mouth after handling contaminated objects without first washing your hands can also transmit diseases; 
  
  
• Foodborne: eating or drinking contaminated or spoiled food or liquid that contain bacteria or other infectious agents; 
  
  
• Animal-borne: contact with animals from bites, scratches, secretions or waste; or 
  
  
• Insect-borne: diseases spread by insects from bites, scratches, or contact with insect excrement or body parts.
  
  

Finding out what infectious diseases are in your workplace

Unlike chemicals that come in labeled containers, biological agents that cause disease are invisible. There are ways, however, to find out what infectious diseases are or are likely to be in your workplace.

Consider environmental factors

The chance of becoming infected with certain diseases is more likely in some types of facilities. For example, water treatment and sewer workers have an increased chance of exposure to hepatitis A, parasites and other infectious agents. Workers who spend time in wooded areas are at higher risk for diseases spread by insect bites, such as Lyme’s disease and other types of biological agents like poison ivy. Infectious diseases are also commonly brought into the workplace by workers, patients, inmates or the public.

There is a connection between poverty and some diseases. For example, tuberculosis spreads more easily where people are crowded together and have little access to health care. Therefore, homeless shelters are places where workers and the homeless have an increased chance of becoming infected.

HIV and hepatitis B can be spread through sharing contaminated needles. Prison inmates have used intravenous drugs at a higher rate than the rest of the public. As a result, the percent of inmates with HIV or hepatitis is much greater than the general population. In addition, since HIV weakens the immune system, people infected with HIV are more likely to have an active case of tuberculosis or other infectious diseases.

Screening

Screening means testing to see if a person has an infection or illness. Screening workers or others is useful to control the spread of some diseases. For example, the Centers for Disease Control and Prevention (CDC) recommends tuberculosis screening for workers in high-risk settings such as prisons, long-term and acute care facilities, shelters and drug treatment programs. Inmates, patients and clients should also be screened for tuberculosis in these high-risk settings.

Notification

Employers should tell their workers about potential exposure to infectious diseases in the workplace. Employers should also inform their workers following a situation that exposes them to an infection. The employer should also provide proper medical treatment after an exposure. Employees should be trained in how diseases are spread, the symptoms of different diseases, and how best to prevent infection.

Workers need to know what to do in case they are exposed to an infectious agent. This includes knowing who to report the exposure to, what tests to take to find out if they have been infected, and what treatment will prevent getting sick. Tests and treatment should be provided as soon as possible after an exposure.

Privacy

There are laws to protect the privacy rights of employees, patients and citizens with respect to medical information. However, a employer can tell workers what precautions are needed to protect against infection. See the isolation precautions at the end of this chapter.

Surveys

As described in Chapter 3, you can get information about illnesses in the workplace by asking co-workers.

Records

Your employer should keep a medical record for each worker who is exposed to infectious diseases on the job. In many cases, the record may include pre-employment and baseline physical examinations and any screening test results. All exposure incidents or further screening or medical tests, preventive therapy and/or treatment should also go into the medical file. Workers should be able to get a copy of their records upon request.

Investigate disease outbreaks

The employer should investigate all outbreaks of communicable diseases in the workplace. Learning how a disease got started and spread will help to prevent further outbreaks.

Check with the local health department

Health departments are a source of information on infectious diseases in your area. County and state health departments keep track of certain communicable diseases. Some diseases, such as active cases of tuberculosis and rabies are "reportable diseases" which must be reported to the health department.