Epidemic

Here the carrier, infected people over a period of time and hence there was no explosive rise in cases.

But over a long duration, many people were affected.

So it is a Common source continuous or repeated exposure epidemic.

Ans. is b i.e., Children are most commonly involved

o The main aim of descriptive epidemiology is to study the distribution of disease in time, place and person.

Time distribution

o There are three kinds of time trends or fluctuations in disease occurence :‑

A.      Short term fluctuations epidemics

B.      Secular trends or long term fluctuations

C.      Periodic fluctuation

Short term fluctuation

o The best known short – term fluctuation in the occurence of a disease is an epidemic.

o There are three major types of epidemics ‑

1) Common – source epidemics

a)       Single exposure or point source epidemics

b)       Continuous or multiple exposure epidemics

2) Propagated epidemics

3) Slow (modern) epidemics

Common source epidemics

q        As name suggests, the source of disease agent is common for all cases.

q        It is of two types.

a) Single exposure or point source epidemics

o The exposure to the disease agent is brief and essentially simultaneous —> single exposure.

• Because disease agent enters into all exposed persons at same time —> the resultant cases all develop within one incubation period of the disease.
• The epidemic curve rises and falls rapidly.
• Because exposure is single (simultaneous) with no further exposure —> No secondary wave (no secondary case).
• Epidemic tends to be explosive, there is clustering of cases within a narrow interval of time. o Point source epidemics are mostly (not always) due to exposure to an infectious agent.
• Examples —> Food poisoning, Bhopal gas tragedy, Minamata disease in Japan, Chernobyl tragedy.

b) Continous or multiple exposure epidemics

o Exposure from the common (same) source is prolonged – continous, repeated or intermittent. o Exposure is not at the same time or place.

o For examle, a prostitute may be a common source in a gonorrhea outbreak, but since she will infect her clients over a period of time there may be no explosive rise in number of case.

• Because disease agent enters into exposed person at different time —> outbreaks continues over more than one incubation period.

o Example –> Outbreak of legionnaire’s disease (respiratory illness) in 1976 in Philadelphia (USA).

Ans. is ‘a’ i.e., Rapid rise and fall; ‘c’ i.e., Explosive 

Ans. is ‘c’ i.e., Be explosive 

Ans. is ‘a’ i.e., Twice the incubation period of the disease since occurrence of the last case 

Ans. is ‘d’ i.e., All cases develop within one incubation period 

Ans. is ‘b’ i.e., Primary case 

The term primary case can only apply to infectious diseases that spread from human to human, and refers to the person who first brings a disease into a group of people—a school class, community, or country.

The index case, however, is the patient in an outbreak who is first noticed by the health authorities, and who makes them aware that an outbreak might be emerging. Even outbreaks of disease that is not spread from human to human, such as Legionnaire’s disease, might have an index case.

Ans. D: Verification of the diagnosis

• Verify the diagnosis-It is the first step
• Establish the existence of an outbreak
• Defining the population at risk
• Define and identify cases and their characteristics
• Describe and orient the data in terms of time, place, and person
• Develop hypotheses
• Evaluate hypotheses
• Evaluation of ecological factors
• Further investigation of populato at risk
• Writing report/ Communicate findings

The steps are presented here in conceptual order. In practice, however, several may be done at the same time, or they may actor be done in a different order. For example, control measures should be implemented as soon as the source and mode of transmission are known, which ma^y be early or late in any particular outbreak investigation.