Infectious disease e.g. cholera, typhoid are common in developing tropical countries. Epidemics are caused also by diseases other than infectious diseases e.g. chemical food contamination air pollution, lung cancer. Steps of investigation of epidemics: 1)confirmation of the diagnosis by clinical and laboratory method. Aims: A.)to determine the correct cause of epidemic disease for examples. To differential diagnosis between hepatitis and yellow fever. The both diseases have the jaundice (yellowish colorations of the eye) *differential diagnosis between Steps of investigation of epidemics:cholera and food poisoning. *differential diagnosis between meningitis and encephalitis. B.)to confirm the diagnosis of the cause of the death of the cases

2)Confirmation the existence of an epidemics by presence of large number of person which have the same complaints of the same case. 3) description of epidemics: It means the identification of affected persons and their characteristic A)with respect to time : it is done by plotting the cases by the time of the onset of symptom using the epidemics curve. Incubation period (I.P): It is the time (minutes, hours, days, months, or even years) between the exposure to agent and the onset of symptomes and sings of the disease. Symptoms:are the complaints of patient by his or her words. Signs: are the objective findings which are seen by doctors, nursing or paramedicans.

Use of I.P.: 1. Determine the source of infection: for example; small pox the patient couid be asked about the movments and contacts with persons dayes befor he got sick 2.determine the period of expouser to contacts:it means the period time equal to the usually incubation period of the infection agent. 3. immunization: certain disease can be prevented by immunization in incubation period. For example: with immunoglobulin (Ig)can be prevented or modify an attack of measles in child which contact with infection. 4. prognosis: in some infection, the prognosis is related to incubation period.the shorter I.P, the worse prognosis e.g. tetanus

Factor that determine the epidemics: 1. onset of the disease. 2. the specific disease which is characterized by its I.P. 3. the time of exposure to the etiological agent. B. With respect to place: It is done plotting the cases by the location of the part of city which they come from using spot map. In use of spotmap, case location can by place of residence, place of work or school attended. C. With respect to person: It is done by tabulating the distribution of cases by age,sex, nationality,occupation, religion, and other characters. Aims: to determine the pin-pointing the exact population at risk.

4. determine of individual epidemics histories: Aim: to allow the classification of exposed persons as to the following. a. source of the infection b. whether ill or not ill c. if ill what is the clinical data, laboratory investigations (results)which help to diagnosis of case. A.) case history: So, take details of each confirmed or suspected cases to obtain complete picture of the epidemic. It include the following.age, sex, name, occupation, place of residence, recent movement, onset of disease, symptoms and sings of disease. B.) Search of additional cases.

5. study of the environmental condition in the identified place e.g. investigation source, method of food preparation and preservation in the area of restaurants. 6. study of source of infection and spread of epidemic This can be done by comparing the percentage of persons exposed to the suspected source or mode of infection among those ill and those not ill. The investigator doctor shouid be know why the epidemic occurred and how the stage come to be set for its occurrence. -In dry months, human movment may be increase the spread of the disease such as meningococcal meningitisand influenza may be facilitated. -At other times, seasonak changes in the temperature and humidity at night facilitate transmission of respiratory organisms among persons sleeping at the room. -Food supplies or water supplies or housing and sanitation should be investigation and local health inspector who has some knowledge of the area is usful person to have on the investigation team.

- as regard to infectious process should be know on the following: 1) the agent of disease and its characteristics. 2)the reservoir (man as a case, or carrier, animals, insects,birds, plants, water or soil). 3. the mode of transmission to the next host. 4. the mode of exit from this reservoir or source. 5. the mode of entery. 6. the susceptibility of the host.

7)mangment of the epidemics: it include the following: a. treatment of cases. The doctor who investigation as an epidemic must also responsibility for treatment of the cases he diagnosis. e.g. in an epidemic of meningitis, plague or cholera need emergency care with rapidly well training additional staff. b. prevention of spread and control measures to plane a complete control program.

☺ many epidemic diseases can be prevented by: Method of prevention of epidemic a. immunization b. isolation of affected individuals and imposition of quarantine to prevent movement in or out of an area. c. improvement of health hygiene through health education d. providing a better water supplies. e. control of vector breeding or killing of vectors f. long term plans for continued vaccination after an initial mass programmed.

c. writing a report: it is usual to write reports after investigation of an epidemic type writing reports: 1.popular account for laymen. Aims :a)to understand the nature of epidemic b) to know the method to prevent spread or recurrence. 2. an account for planners in the ministry of health. Aims: to know the necessary steps are taken to limit the outbreak or prevent recurrent. 3. scientific report Aim: to teaching a medical staff about medical control. - during the acute phase of epidemic, it is necessary to keep the individual at special risk (e.g. contact) under the surveillance. - after the epidemic is under control, it is necessary to keep the immunity under surveillance to detect further rises in incidence or to insure effective control measure -keep all links of chain (infectious agent, reservoir, mode of transmission and level of immunity )under the close observation.

-sources of information for surveillance: 1. notification of illness by medical staff, school teachers or heads of families 2. certification of death by medical aurthrities. 3. data from other source e.g. public health laboratories.