What makes something infectious?
Some diseases are contagious - they spread by contact between people. Infectious diseases spread by infectious agents - bacteria and viruses for instance. Contagious diseases are infectious, but not all infectious diseases are contagious.
Infectious agents are transmitted from person to person in any of a hundred ways: When a sick person sneezes, tiny particles of water are sprayed into the air, where some may enter other people through the mouth or nose. Liquids are effective vectors of disease because microorganisms can live in them more readily that on dry surfaces (generally speaking). Infectious medical waste is often (not always) wet. One job of the waste manager is to keep people (employees, patients, visitors) from becoming infected from the waste.
An infectious substance is material that contains (or can be expected to contain) a microbe or particle that can cause disease. Waste with an infectious substance is infectious waste. Another term is biomedical waste. Medical waste can be a reservoir of pathogens.
Cultures of biological materials (cells, viruses) are used by researchers and biotech operations. They are intentionally grown, “cultured”. Some biological products made to treat or prevent disease are infectious. Specimens from human or animal bodies can also be infectious.
Is there a difference in hazard level between (1) a tissue that a person with a common cold blew his nose into and (2) bandages that absorbed secretions from a patient with tuberculosis. Of course there is. In the absence of clear legal or regulatory lines, it falls to human judgement to identify what is infectious waste of concern. Classifying waste as “infectious” is done by judgement of the healthcare professional. Infection control officers in hospitals and safety managers at biotechnology labs know there are grades of risk posed by infectious waste. The most highly infectious waste comes from microbiological cultures. The EPA has said that cultures and stocks with viable biological agents that have been artificially cultivated to elevated numbers pose the highest disease risk of any form of medical waste. Even more worrisome that material contaminated with fluids from tuberculosis patients is Sputum cultures of TB.
Compared with hazardous waste (RCRA waste), there is little clarity the definition of infectious waste in a legal sense. Lawmakers and regulatory agencies have trouble defining what items are infectious, and distinguishing between waste with dangerous pathogens and waste with relatively bening pathogens. It falls to the waste management engineer to use the precautionary principle and good judgement in deciding courses of action with regard to storage, treatment, and disposal.
Microorganisms that cause disease are called pathogens. Most microorganisms are not pathogens; they are benign. Bacteria are single-cell organisms. The cells are similar in many ways to the cells that make up our bodies. Some bacteria cause disease. Mycobacteria are a genus of bacteria that include pathogens that cause tuberculosis and leprosy. Bacteria are susceptible to antibiotics which kill them or stop them from reproducing, and antibiotic materials are widely used in disinfection and sterilization processes. Rickettsia are a type of bacteria that live inside cells of other organisms. Viruses are clumps of genetic material surrounded by a protein coat. They are not truly alive in that they don’t eat or use energy. Once viruses get inside other cells, they can hijack the cellular processes and cause replication of themselves. This causes disease. Viruses are not susceptible to antibiotics, but can be denatured or deactivated by high temperatures or harsh chemicals.
Mold and mildew are both fungi. They are usually not harmful or toxic to people. (A few forms of mold are dangerous.) Fungi produce spores to reproduce. The spores have thick walls and are hardier than most fungi cells. When people want to eliminate fungi they concentrate on killing spores.
Prions are infectious proteins; they strike fear into the hearts of infection control officers. They can cause fatal brain diseases, and cannot be eradicated by washing, most chemical disinfectants, or boiling water. Scientific American magazine says prions should be in the “Hard-to-Kill Hall of Fame”. Like viruses they are not really alive. Much is unknown about how they cause disease. If you suspect your waste has prions in it, call in an expert. There is evidence that alkaline hydrolysis processes used on animal carcasses eradicate them, but much is not clear.
Some bacteria also produce spores called endospores. These allow the bacterial population to survive changes in the environment - to wait out harsh conditions before coming back to live as regular bacteria.
Before prions came to the limelight, endospores were considered the hardest pathogens to destroy. While heating a material to 150 °F for 20 minutes will kill most bacteria and viruses present, endospores can survive. This is why autoclaves operate at temperatures of 250 °F and higher.
Industrial hygienists and public health pros generally consider these pathogens the hardest to kill, in order from hardest to easiest:
Disease-causing parasites, such as Giardia and Cryptosporidium, are resistant to disinfection and are usually rated between the mycobacteria and the viruses.
Prions are the big unknown here, partially because they have been discovered more recently, methods to detect them are not widespread, and it is not clear which diseases are caused by prions. However, experts think they should be at the top of the list (harder to destroy than bacterial spores) or close to the top.
Conventional pathogens: Cause disease in healthy people who don't have immunity. Staph infections, strep infections, tuberculosis, influenze are examples.
Conditional pathogens: Cause disease in people with reduced resistance to infection or when implanted directly into tissue.
Opportunistic pathogens: Cause disease in people with severely weakened immune systems.
Is segregating infectious or pathological waste the same as quarantining an area?
No. The word quarantine is a legal and public health term. It is the forced legal restriction of people or animals to prevent the spread of communicable disease. The quarantine order specifies a period of time which those affected are not permitted to mix with general society. The idea of quarantines started centuries ago. For instance, when a ship came into a harbor, the officials in the new city might quarantine everyone on the ship for fear of plaque. After a certain period of time if the people did not display symptoms, they were released from quarantine. With advances in diagnostic technologies quarantines are employed less often than they once were.
Medical isolation is a related term for when people with communicable diseases are kept away from others. This is closed in spirit to segregation of medical waste, but still not the same thing. Patients in medical isolation usually either get better or worse over time and the time of isolation is limited.
Hospital-acquired infections (aka nosocomial infections) are a big concern for healthcare facilities. The biggest source of possible infection at hospitals and clinics isn't medical waste; it's people (workers, visitors, patients.) While many hospitals have infection control personnel on staff, waste managers also get involved when it comes to isolating waste and making sure waste does not pose an undue risk to patients, staff, and visitors. See our page on nosocomical infections.
Transportation regulatory agencies have their own classifications. The U.S. Department of Transportation and the International Air Transportation Association have defined Category A and Category B. Category A is waste that might cause permanent disability or life-threatening disease. Category B is less dangerous. Where to draw the line is largely a judgment call on behalf of transport professionals and regulators. The dangerousness of a waste is due to the presence of pathogens and the type of pathogens, obviously. But other factors include the nature of the bulk waste (liquid, slurry, solid, particle size) and packaging.
Transportation authorities look at infectious human or animal tissue and laboratory cultures as items to be classified as Category A or Category B. There are different safety measures required for each category. See our page on transportation.