Fomites Health Dictionary

The process by which a disease is transmitted via micro-organisms from one person to another. The micro-organism may be a bacterium (see BACTERIA), a RICKETTSIA, a VIRUS, a protozoon – single-celled animal organism – or a metazoon – multicellular animal organism. Invasion of the body by a metazoon (e.g. by an intestinal worm) is more often known as an infestation.

The skin is an important protection against micro-organisms entering the body tissues. A large measure of protection is a?orded by the factors which ensure IMMUNITY against diseases.

Modes of infection The infective material may be transmitted to the person by direct contact with a sick person, when the disease is said to be contagious, although such a distinction is purely arti?cial. Di?erent diseases are especially infectious at di?erent periods of their course. Protecting people can be di?cult, since some diseases are infectious before the patient shows any symptoms (see INCUBATION).

Infection may be conveyed on dust, in drinking-water, in food (particularly milk), in the body’s waste products and secretions, or even on clothes and linen which have been in contact with the infected individual (called fomites).

Some people who have recovered from a disease, or who have simply been in contact with an infectious case, harbour the infectious agent. This is particularly the case in typhoid fever (see ENTERIC FEVER), the bacillus continuing to develop in the gall-bladder of some people who have had the disease for years after the symptoms have disappeared. In the case of CHOLERA, which is ENDEMIC in some developing countries with hot climates, 80 per cent or more of the population may harbour the bacillus and spread infection when other circumstances favour this. Similarly in the case of DYSENTERY, people who have completely recovered may still be capable of infecting dust and drinking-water by their stools. DIPHTHERIA and meningococcal MENINGITIS, which is particularly liable to infect children, are other examples.

Flies can infect milk and other food with the organisms causing typhoid fever and food poisoning. Mosquitoes carry the infective agents of MALARIA, DENGUE and YELLOW FEVER, these undergoing part of their development in the body of the mosquito. Fleas convey the germ of plague from rats to humans, and lice are responsible for inoculating TYPHUS FEVER and one form of RELAPSING FEVER by their bite. A tick is responsible for spreading another form of relapsing fever, and kala-azar (LEISHMANIASIS) is spread by the bites of sand?ies.

Noti?able diseases Certain of the common and most serious infectious diseases are noti?able in the United Kingdom. A doctor diagnosing someone infected by a noti?able disease must inform the authorities. For the current list of noti?able infectious diseases in the UK, see the main entry for NOTIFIABLE DISEASES.

Prevention is an important aspect of the control of infectious diseases, and various steps can be taken to check the spread of such infections as dysentery, tuberculosis, malaria and others. (See also IMMUNITY; INCUBATION.)... infection

A common contagious itching disease caused by Sarcoptes scabei hominis (see SARCOPTES) which can live only on human skin. The fertilised female burrows into the skin surface, creating a tunnel within the stratum corneum in which she deposits 2–3 eggs per day, as well as faecal pellets which contain the ALLERGEN which initiates the immune reaction responsible for symptoms. The adult female is just visible. Eggs hatch within 3–4 days, producing larvae. After successive moults these become adult mites and the 15-day lifecycle re-starts. A rapid build-up of mite numbers is not noticed by the host until an immune response induces itching after about six weeks. Subsequently, scratching reduces the adult mites to a dozen or fewer. Scabies is spread by skin-to-skin contact, usually via the hands: it thus spreads in a family or sexual setting. Though most common in young adults, scabies can affect any age-group.

Typically the patient complains of widespread severe itching, worse when the body is warm after a bath or in bed. Burrows are visible as wavy black lines 3–5 mm long in the skin of the hands, wrists or sides of the feet. The intensity of the rash depends on the immune response. Papules, pustules, crusts and excoriations are seen on the hands and there may be a widespread eczematous (see DERMATITIS) or urticarial (see URTICARIA) rash elsewhere. Papules or even nodules on the PENIS and SCROTUM are characteristic. In infants, burrows occur on the palms and soles. Diminished immune response in old age, DOWN’S (DOWN) SYNDROME, etc. lead to a type of scabies which is less itching and more scaly. Rarely, absence of immune response causes a mite-saturated, generalised scaly dermatitis (Norwegian scabies). Admission of such a patient to hospital may result in an outbreak of scabies in other patients, sta? and visitors caused by mite-infested airborne scale.

Treatment MALATHION 0·5 per cent aqueous lotion, or PERMETHRIN 5 per cent cream, applied to the whole body, except the head, for 24 hours and then washed o? cures the infection. In infants the head and neck should be included. The secondary eruption may take 2– 3 weeks to settle completely and 10 per cent crotamiton cream is used during this period. It is essential that all intimate contacts be treated simultaneously. FOMITES need not be treated.... scabies

n. (pl. fomites) any object that is used or handled by a person with a *communicable disease and may therefore become contaminated with the infective organisms and transmit the disease to a subsequent user. Common fomites are towels, bed-clothes, cups, and money.... fomes

Any mechanism by which a susceptible human host is exposed to an infectious or parasitic agent. These mechanism are:- 1. Direct transmission Direct and essentially immediate transfer of infectious agents (other than from an arthropod in which the organism has undergone essential multiplication or development) to a receptive portal of entry by which infection of humans may take place. This may be by touching, as in kissing, sexual intercourse or biting (direct contact); or by the direct projection of droplet spray onto the conjunctivae, or onto the mucous membranes of the nose or mouth during sneezing, coughing, spitting or talking (usually not possible over a distance greater than 3 ft) (droplet spread); or, as in the systemic mycoses, by direct exposure of susceptible tissue to soil, compost or decaying vegetable matter that contains the agent and where it normally leads a saprophytic existence. 2. Indirect transmission (a) Vehicle-borne Contaminated materials or inanimate objects such as toys, handkerchiefs, soiled clothes, bedding (fomites), surgical instruments or dressing (indirect contact); water, food, milk, biological products including serum and plasma, or anysubstance serving as an intermediate means by which an infectious agent is transported and introduced into a susceptible host through a suitable portal of entry. The agent may or may not have multiplied or developed in or on the vehicle before being introduced into man. (2) Vector-borne (i) Mechanical:- Includes simple mechanical carriage by a crawling or flying insect through soiling of its feet or proboscis, or by passage of organisms through its gastrointestinal tract. This does not require multiplication or development of the organism. (ii) Biological:- Propagation (multiplication), cyclic development, or a combination of them (cyclopropagation) is required before the arthropod can transmit the infective form of the agent to man. An incubation period (extrinsic) is required following infection before the arthropod becomes infective. Transmission may be by saliva during biting, or by regurgitation or deposition on the skin of agents capable of penetrating subsequently through the bite wound or through an area of trauma following scratching or biting. This is transmitted by an infected invertebrate host and must be differentiated for epidemiological purposes from simple mechanical carriage by a vector in the role of a vehicle. An arthropod in either role is termed a vector. (c) Air-borne The dissemination of microbial aerosols with carriage to suitable portal of entry, usually the respiratorytract. Microbial aerosols are suspensions in air of particles consisting partially or wholly of microorganisms. Particles in the 1 to 5 micron range are quite easily drawn into the lungs and retained there. They may remain suspended in the air for long periods of time, some retaining and others losing infectivity of virulence. Not considering as airborne are droplets and other large particles, which promptlysettle out; the following are airborne, their mode of transmission indirect: (i) Droplet nuclei: Usually the small residues which result from evaporation of droplets emitted by an infected host. Droplet nuclei also may be created purposely by a variety of atomising devices, or accidentally, in microbiology laboratories or in abattoirs, rendering plants, autopsy rooms, etc. They usuallyremain suspended in the air for long periods of time. (ii) Dust: The small particles of widely varying size which may arise from contaminated floors, clothes, beddings, other articles; or from soil (usually fungus spores separated from dry soil by wind or mechanical stirring). Note: Air conditioning and similar air circulating systems may play a significant role in air-borne transmission (e.g. Legionnaire’s disease).... transmission

Winter vomiting disease, or epidemic nausea and vomiting, is a condition caused by subtypes of the genus Norwalk-like virus and is characterised by nausea, vomiting, diarrhoea and giddiness, which occurs during the winter. Outbreaks of it usually involve whole families or may affect communities like schools. The incubation period is 24–48 hours, and attacks seldom persist for more than 72 hours. In England and Wales in 2000, more than 1,600 infections were reported compared to more than 16,400 cases of salmonella infections and 56,420 of CAMPYLOBACTER. However, in England it is estimated that around 1,500 times more people are infected in the community than are reported. Humans are the only known hosts of the virus and infection can be acquired via contaminated food or water or, more commonly, from an infected individual via the faeco-oral route, aerosol-spread and FOMITES.... winter vomiting disease