The above inform ation represents the total number of cases of salmonellosis ass

Question

The aboveinformation represents the total number of cases of salmonellosis associated with a chicken meal during the month of January 2010 in a city of one million inhabitants, of which is estimated that 80% eat chicke.

1. What is the cumulative incidence for the period of the study?

2. What is the incidence rate for the period of Jan. 1st- Jan. 13th inclusively?

3. What is the prevalence of salmonellosis for the month of January?

4. Between January 15th and January 18th inclusively, 22 people who suffered from salmnellosis reported that they had eaten chicken distributed by the company "Good Chicke". It is estimated that among costumers of chicken, 10% consume chicken of the "Good Chicke" brand. What is the relative risk of salmonellosis associated with consumption of the "Good Chicken" brand?

Outbreak of Salmonellosis in January 2010 40 35 30 25 6 20 E 15 3838 37 32 12 Z 10 8 5 0 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728 293031 January 2010 The above information represents the total number of cases of salmonellosis associate

Explanation / Answer

1. Cumulative incidence of salmonellosis during January 2010 was 180 cases out of 10lakh at risk of salmonellosis (80% of 1 million) = 180/1000000 = 0.00018 or 0.018% of the population suffered from salmonellosis. It is referred as cumulative incidence.

2. Incidence rate is number of persons suffered from salmonellosis on particular days.

4*1+5*1+9*2+10*2+14*8+15*32+16*8+17*38+18*37+19*12+20*6+21*2+26*1=> 5+5+18+20+112+480+128+646+666+228+120+42+26 = 2496

incidence rate is 180/2496 = 0.072 per 31 days of observation.

3. Prevalence of salmonellosis in January is 180/10000000 = 0.000018.

4. relative risk is calculated by risk ratio. Risk ratio is

Cumulative incidence in exposed group / cumulative incidence in unexposed group

exposed group refers to the number of people suffering from salmonellosis between Jan15th to 18th who have eaten good chick. It represents 22 out of 145.

Unexposed group refers to the number of people sufffering from salmonellosis between Jan15th to 18th who have not eaten good chick. It represents 123 out of 123.

Risk ratio associated with consumption of good chick = 22/145 / 123/123 = 0.1517

As the risk ratio is less than 1, it indicates the decreased risk of salmonellosis in the exposed group.

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