The data secured by these reports should be immediately classified and tabulated by the health authorities so that the maximum information will be revealed. They first of all should be classified according to disease. Each case reported should be located upon a spot map of the area. Summaries of the total cases of each disease reported by days, weeks or months should be kept constantly up to date, making the necessary ad ditions to these tables each day. Thus the health authorities can constantly keep their fingers upon the pulse of disease preva lence and instantly recognize any epidemic in its incipiency and in addition deal effectively with endemic disease. Many health authorities in addition to the daily summaries above noted, also daily post the cases of diseases which may be milk borne against the dealer from whom their milk was secured, and thus they can learn immediately of a milk-borne outbreak. If these reports are only used to prepare tables of figures to show past history of disease prevalence, very little actual service will result from reporting.
In general we may say that the morbidity information will be put to the following uses: (a) It shows the geographical location of sources or foci of infection.
(b) Enables the health authorities, by the investigation of the cases reported, to secure epidemiological information of occur rence, distribution and prevalence of disease; ascertain missed cases and carriers and prevent the further spread of disease.
(c) Enables proper treatment to be provided for those finan cially unable to secure it.
(d) Indicates the necessary preventive measures.
(e) Gives the history of a given disease for a series of years, from which the endemic index may be computed.
(j) In the case of occupational diseases, it shows the location of conditions causing disease or injury.
For purposes of comparison morbidity information is ex pressed by several rates, as follows: (a) The crude morbidity rate. This is the number of cases of a given disease occurring during a year per I000 or ro,000 of the total population. This is open to the same disadvantages as crude rates in general.
(b) The specific morbidity rate. These are of a value similar to specific death rates. Diseases whose incidence is limited to certain age groups should also be expressed in rates of the number of cases per i000 persons in the population of that age or class.
(c) Fatality rates. These may be expressed as the number of deaths per roo cases or as the number of cases to each death. They are the same as the case mortality ratios previously noted. Owing to failures to report all cases they are usually too high (Figs. 133, 134) For areas of small size with small or moderate populations, small charts will enable the health authorities to keep in touch with the daily or weekly incidence of communicable diseases and detect epidemics in their incipiency. On the other hand, where a large number of geographical units must be supervised a more rapid method of ascertaining fluctuations of disease prevalence from the normal or endemic prevalence is afforded by comparison of the monthly summaries with the so-called endemic index of a disease for the area under consideration. This is the average monthly incidence of the reported cases of the disease in a given geographical unit, exclusive of cases rising in epidemics. Such standards of course require occasional revision. By their employment the beginning of an epidemic can be promptly noted.