Infectivity Health Dictionary

An infection by any one of around 200 viruses, with about half the common-cold infections being caused by RHINOVIRUSES. Certain CORONAVIRUSES, ECHOVIRUSES and COXSACKIE VIRUSES are also culprits. The common cold – traditionally also called a chill – is one of several viral infections that cause respiratory symptoms and systemic illness. Others include PNEUMONIA and GASTROENTERITIS. Colds are commoner in winter, perhaps because people are more likely to be indoors in close contact with others.

Also called acute coryza or upper respiratory infection, the common cold is characterised by in?ammation of any or all of the airways – NOSE, sinuses (see SINUS), THROAT, LARYNX, TRACHEA and bronchi (see BRONCHUS). Most common, however, is the ‘head cold’, which is con?ned to the nose and throat, with initial symptoms presenting as a sore throat, runny nose and sneezing. The nasal discharge may become thick and yellow – a sign of secondary bacterial infection – while the patient often develops watery eyes, aching muscles, a cough, headache, listlessness and the shivers. PYREXIA (raised temperature) is usual. Colds can also result in a ?are-up of pre-existing conditions, such as asthma, bronchitis or ear infections. Most colds are self-limiting, resolving in a week or ten days, but some patients develop secondary bacterial infections of the sinuses, middle ear (see EAR), trachea, or LUNGS.

Treatment Symptomatic treatment with ANTIPYRETICS and ANALGESICS is usually su?cient; ANTIBIOTICS should not be taken unless there is de?nite secondary infection or unless the patient has an existing chest condition which could be worsened by a cold. Cold victims should consult a doctor only if symptoms persist or if they have a pre-existing condition, such as asthma which could be exacerbated by a cold.

Most colds result from breathing-in virus-containing droplets that have been coughed or sneezed into the atmosphere, though the virus can also be picked up from hand-to-hand contact or from articles such as hand towels. Prevention is, therefore, di?cult, given the high infectivity of the viruses. No scienti?cally proven, generally applicable preventive measures have yet been devised, but the incidence of the infection falls from about seven to eight years – schoolchildren may catch as many as eight colds annually – to old age, the elderly having few colds. So far, despite much research, no e?ective vaccines have been produced.... cold, common

A highly contagious infectious disease, also called whooping cough, which mainly affects infants and young children. The main features of the illness are bouts of coughing, often ending in a characteristic “whoop”. The main cause is infection with BORDETELLA PERTUSSIS bacteria, which are spread in airborne droplets.

After an incubation period of 7–10 days, the illness starts with a mild cough, sneezing, nasal discharge, fever, and sore eyes. After a few days, the cough becomes more persistent and severe, especially at night. Whooping occurs in most cases. Sometimes the cough can

cause vomiting. In infants, there is a risk of temporary apnoea following a coughing spasm. The illness may last for a few weeks. The possible complications include nosebleeds, dehydration, pneumonia, pneumothorax, bronchiectasis (permanent widening of the airways), and convulsions. Untreated, pertussis may prove fatal.

Pertussis is usually diagnosed from the symptoms. In the early stages, erythromycin is often given to reduce the child’s infectivity. Treatment consists of keeping the child warm, giving small, frequent meals and plenty to drink, and protecting him or her from stimuli, such as smoke, that can provoke coughing. If the child becomes blue or persistently vomits after coughing, hospital admission is needed.

In developed countries, most infants are vaccinated against pertussis in the 1st year of life. It is usually given as part of the DPT vaccination at 2, 3, and 4 months of age. Possible complications include a mild fever and fretfulness. Very rarely, an infant may have a severe reaction, with high-pitched screaming or seizures.... pertussis

a person with a communicable disease in whom the symptoms and signs are so minimal that either there is no request for medical assistance or the doctor fails to make the diagnosis. The patient usually has partial immunity to the disease, but since the infecting organisms are of normal virulence, nonimmune contacts can be affected with the full manifestations of the illness. The period of infectivity is confined to the shortened duration of the illness (in contrast to a *carrier, in whom the pathogen is present without necessarily causing any ill effect). Alternatively, the subject has had the disease but retains some of the pathogens (e.g. in the throat or bowel) and so acts as a continuing reservoir of infection.... missed case

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

any one of a class of drugs used in the treatment of HIV infection and *AIDS. Used in combination with other *antiretroviral drugs, they act by inhibiting the action of protease, an enzyme produced by HIV that cleaves two precursor proteins into smaller fragments. These fragments are required for viral growth, infectivity, and replication. Protease inhibitors include atazanavir, indinavir, lopinavir and ritonavir (which are used in combination), saquinavir, and tipranavir. Side-effects include nausea, vomiting, diarrhoea, and rashes; these drugs are also associated with hyperglycaemia and *lipodystrophy. See also boceprevir.... protease inhibitor