Throughout history man has faced the spread of infection, pondering its causes and how to treat it or prevent it. Infections have been known to affect major segments of the population, as did the plague in the Middle Ages. Although important advances have been made in understanding and treating infection, the threat of infection looms as large as it ever has. Newer enemies in the battle of infection emerge such as HIV and hepatitis C virus (HCV). Once-conquered enemies become resistant to treatment, as it the case of Mycobacterium tuberculosis and methicillin-resistant Staphylococcus aureus. Healthcare personnel typically encounter numerous patients on a daily basis, many of whom may be harboring these or other agents of infection. Measures to prevent the spread of infection must be taken in the course of treating all patients.
Below we explain the infection process and describe infection control measures needed to protect healthcare patients, staff, visitors, and those who do business with healthcare facilities.
What Is Infection?
Our environment is full of microorganisms (microscopic organisms) referred to as microbes. Microbes include bacteria, fungi, protozoa, and viruses. The majority of microbes are nonpathogenic, meaning they do not cause disease under normal conditions. Microbes that are capable of causing disease (ie., pathogenic) are called pathogens. If a pathogen invades the body and the conditions are favorable for it to multiply and cause injurious effects or disease, the resulting condition is called an infection. The pathogen responsible for causing the infection is referred to as the infectious or causative agent. Infection can be local (restricted to a small area of the, body) or systemic, in which the entire body is affected.
Some pathogenic microbes cause infections that can be spread from person to person. These infections are called communicable infections and the diseases that result are called communicable diseases. A division of the U.S. Public Health Service called the Centers for Disease Control and Prevention (CDC) is charged with the investigation and control of various diseases, especially those that are communicable and have epidemic potential. The CDC recommends safety precautions to protect healthcare workers and others from infection.
Approximately 5 % of patients in the United States are exposed to and contract some sort of infection after admission to a hospital or other healthcare facility. These hospital or healthcare facility-acquired infections are called nosocomial infections. Nosocomial infections can result from contact with infected personnel, other patients, and visitors, or contaminated equipment. The most common nosocomial infection in the United States is urinary tract infection. The Hospital Infection Control Practice Advisory Committee (HICPAC), established in 1991, advises the CDC on updating guidelines regarding prevention of nosocomial infection.
Source Of Infection
The source is the origin of infectious microorganisms, also called the reservoir. Sources of infectious microbes include infected humans or anima1s and contaminated articles and equipment. In a healthcare setting, human sources of infectious microbes can be patients, personnel, or visitors, and can include those with active disease, those whose disease is in the incubation period, and those who are chronic carriers of a dis- ease. Another potential source of infectious microbes is a person’s own normal flora (microorganisms that normally live on the skin and other areas of the human body).
Inanimate objects such as contaminated equipment can be a major source of infection in a healthcare setting. Whether or not an inanimate source is capable of transmitting infection depends upon the amount of contamination, the viability or ability of the organism to survive on the source, the virulence or degree to which an organism is capable of causing disease, and the amount of time elapsed between when the source was contaminated and when it was contacted.
For example, the virus that causes hepatitis B is much more virulent, or capable of causing disease from a small amount of infective material, than HIV, the virus that causes AIDS. It is also more viable, meaning it is capable of surviving longer on surfaces than is HIV. However, if a long enough time elapses from the time of contamination until contact by a susceptible host, the microbe is no longer alive and is not capable of transmitting disease.
Modes Of Transmission
There are five basic modes or routes of infection transmission: contact, droplet, airborne, vehicle, and vector. The same microbe can be transmitted by more than one route.
Contact transmission is the most frequent mode of infection transmission. There are two types of contact transmission, direct transmission and indirect transmission.
Direct contact transmission involves direct, physical transfer of a pathogenic microbe to a susceptible host through close or intimate contact such as touching or kissing.
Indirect contact transmission involves personal contact by a susceptible host with contaminated inanimate objects such as patient bed linens, clothing, dressings, and eating utensils. It includes contact with phlebotomy equipment such as gloves, needles, specimen tubes, and phlebotomy carts and trays. It also includes less obvious contaminated objects such as doorknobs and faucet handles. The transfer of infectious microbes from contaminated hands to a susceptible host is also considered indirect contact transmission.
Droplet transmission involves the transfer of the infective microbe to the mucous membranes of the nose or mouth or the conjunctiva (mucous membranes) of the eyes of a susceptible individual through sneezing, coughing, or talking by an infected per- son. Droplet transmission can also occur during procedures such as suctioning and throat swab collection. It differs from airborne transmission in that droplets do not travel more than 3 feet, and do not remain suspended in air.
Airborne transmission involves dissemination of droplet nuclei. Droplet nuclei are the residue of evaporated droplets generated by sneezing, coughing, or talking. Infectious microbes within droplet nuclei can remain viable even though suspended in the air or in dust particles for long periods. Microbes carried in this manner can become widely dispersed before being inhaled by or deposited on a susceptible host. For this reason, special air handling and ventilation are required for rooms of patients having infections with airborne transmission. Persons entering the room must wear a snug-fitting mask with a special filter. M. tuberculosis, rubeola virus, and varicella virus are the most common microorganisms transmitted by the airborne route.
Vector transmission involves the transfer of the microbe by an insect, arthropod, or animal. An example of vector transmission is the transmission of malaria by a mosquito or the plague by rodent fleas.
Vehicle transmission involves the transmission of the infective microbe through contaminated food, water, or drugs. Examples of vehicle transmission are salmonella infection from handling contaminated chicken and shigella infection from drinking contaminated water. The transmission of hepatitis and HIV through blood transfusion is also considered vehicle transmission.
A susceptible host is someone who has decreased ability to resist infection. Susceptibility is affected by age, health, and the immune status of the individual. For example, newborns whose immune systems are not yet developed and old people whose immune systems are no longer functioning properly are more susceptible to infections. In addition, disease, antibiotic treatment, and immunosuppressive drugs may compromise a person’s resistance to infection. Procedures such as surgery, anesthesia, and insertion of catheters can also leave a patient more susceptible to infection. Recovery from a particular virus or vaccination against a virus also affects susceptibility. A healthy person who has received a vaccination against a disease-causing virus, or who has recovered from infection with a particular virus, has developed antibodies against that virus and is considered to be immune, or unlikely to develop the disease.
Breaking The Chain Of Infection
Breaking the chain of infection means stopping infections at the source, eliminating means of transmission, and reducing or eliminating the susceptibility of potential hosts. Ways to prevent transmission of infectious microbes are proper hand washing; use of gloves, gowns, masks, and other protective equipment when indicated; proper waste disposal; isolation procedures; insect and rodent control; and decontamination of surfaces and instruments. Susceptibility of potential hosts can be reduced through proper nutrition, reduction of stress, and immunization against common pathogens.