CONTACT TRANSMISSION I. By contact transmission we mean the transfer of infective secretions or excretions from one person to another with the lapse of but a short space of time during which interval the in fective agents are subject to little or no attenuation. From the great variety of infective agents transmitted by this means, as well as the constancy with which opportunities for this transference are encountered, it is the most important of the routes of infection.
2. Means of Contact we may say that contact transmission is accomplished through the con tinous universal commerce in the body secretions and excre tions. This commerce is accomplished by the following agencies.
(a) Mouth Spray or Droplet Infection.—Every person in talking, coughing, or sneezing, emits from the mouth with more or less explosive force a fine spray of saliva, which will of course contain suspended in it, micro-organisms from the mouth, nasopharynx, or respiratory passages. These particles remain suspended in the air for some time by reason of their buoyancy, but tend to settle out. Air currents may distribute them for short distances. They will of course ultimately evaporate and with evaporation, desiccation of the micro-organisms will occur. The survival of the droplets will of course be longer in a cold humid atmosphere than in a warm dry atmosphere. In a more or less stagnant atmosphere, a quiescent individual may cover a radius of about six feet with these droplets. These are prob ably of greatest importance when expelled directly onto the body surface of another individual, although the buoyant particles are undoubtedly responsible for the old belief in air borne infection.
(b) Hands and Fingers contaminated with Secretions are undoubtedly the most important agencies in contact infection. Their importance is both from the standpoint of distribution and collection. Fingers are naturally exploratory in their habits, reaching all portions of the body surface and the body orifices of their owner, thus becoming contaminated with the secretions and excretions, and transferring these to objects later handled.
In turn from such objects, the infective secretions of other persons similarly distributed, are collected and introduced into or onto the body of their owner. The fingers of a non infected person may also transfer infective agents to a third person. It is for this reason that the habits of avoiding the unnecessary introduction of the fingers into the mouth and nose, as well as the habit of washing the hands before eating, are of paramount hygienic importance.
(c) A certain communism in small objects was formerly very popular, but fortunately today is looked upon with little esteem. This was the practice of furnishing common articles in public places for intimate personal service, such as drinking cups, towels, combs, pencils and numerous other objects. The intimate use to which these are put renders their contamination by excretions and secretions practically unavoidable, which will be effectively transferred to the next person using them. Des pite the reduction in recent years of objects, such as drinking cups, which are directly contaminated with secretions, it is prac tically impossible to always avoid objects which are continually contaminated with human secretions.
(d) Lastly, direct approximation of the body surfaces of two different individuals, such as that which occurs during a hand clasp, kissing or sexual intercourse, will effectively transmit infective agents present on one to the other, under circum stances which of course are altogether favorable to the infective agents.
The term direct contact transmission is applied to the second and the last of these agencies, as well as to certain aspects of the first. In these of course, no intermediate objects par ticipate in the transfer. Distinction between indirect contact transmission and fomites transmission has already been made.
3. Importance of Contact Transmission with Different Infec tive Agents.—According to the importance of contact in the transmission of different infective agents, we can distinguish several groups of diseases.