epidemiology

Case Study: Outbreak in Littletown

Background

One of the pathogens which can be present in food is Escherichia coli O157:H7 or E. coli. This disease can cause bloody diarrhea and severe fluid loss in affected individuals. In children under five years of age and the elderly, the infection can cause a complication called hemolytic uremic syndrome, in which the red blood cells are destroyed and the kidneys fail. On average, people will show symptoms between four to six days after eating contaminated products. The source of this bacteria is often contaminated meat that is handled incorrectly or not cooked hot enough to eliminate any E. coli. The disease can also spread through a food-handling facility when workers do not wash their hands correctly after handling meat products. In this way it can spread to food products which do not contain meat. Since the symptoms can have different causes not related to this bacteria, tests need to be conducted to determine the presence of E. coli. To test for this bacteria, stool samples are taken and checked for the presence of this bacteria using gel electrophoresis, which can be used to identify specific proteins or DNA fragments unique to Escherichia coli O157:H7. To determine if an outbreak did occur or if this is an isolated incident, the numbers of the population need to be compared to those of previous years. In order to narrow down the source of the outbreak, interviews need to be conducted with patients suffering from this disease.

Data

Littletown, New Hampshire, is a small community in the White Mountains. The town has 205,692 inhabitants year-round although this number increases during summer vacation, fall, and winter ski season. The city has four hospitals which are work together in a healthcare system. One hospital, Northern Lights, serves the population in the northern part of the city. The hospital to the east is Ocean Breeze. Mountain View serves the west side of the city while Whispering Pines serves the south side. The population is mainly working middle class with an average age of 37 (see table below for demographics). Many younger people have left the area to go to college or start careers in different parts of the state. The city has four retirement homes and has a city water supply from the nearby lake which serves the entire city.

Age range	Percentage of the population	Total number of people in this age group
0-10	15	30,853
10-20	10	20,569
20-30	8	16,455
30-40	28	57,594
50-60	23	47,309
70-80	11	22,626
80 and higher	5	10,285

Table 1: Percentage of the population of Littletown New Hampshire per age group

The Results

Late April 2018 the hospitals in and around Littletown, New Hampshire, started to notice that they were receiving a lot of patients suffering from fever, diarrhea, and fluid loss. The data they collected was compared to data from previous years to determine if there was a seasonal effect or if this was, indeed, an epidemic. The time period used was from April 18 – March 18. Affected people were people showing more than four diarrhea events per day combined with a bloody stool. Samples from individuals were taken and tested for the presence of Escherichia coli O157:H7. Only individuals which had the bacteria in their samples are shown in the table. In order to consider this an outbreak, there needs to be a doubling of the percentage of total number of people infected in a particular age group.

One other way to see how detrimental an epidemic might be is to determine the morbidity rate. This is the percentage of the population dying from this disease. This can either be done by looking at the total number of people dying of this disease or by looking at specific age groups.

Age range	Number of people showing symptoms in 2017	Number of people dying who were suffering from these symptoms in 2017	Number of people showing symptoms in 2018	Number of people dying who were suffering from these symptoms in 2018
0-10	7	4	18	12
10-20	5	1	7	4
20-30	3	0	19	6
30-40	15	0	31	11
50-60	12	2	15	4
70-80	10	3	9	2
80 and higher	2	1	1	1

Table 2: Percentage of the population of Littletown New Hampshire suffering from symptoms and dying from the symptoms per age group in the time period from April 18 – March 18

Name of the hospital	Northern lights	Ocean breeze	Mountain view	Whispering pines
Number of affected cases	60	28	10	2

Table 3: Total number of cases in each of the area hospitals

Source of the Outbreak

In order to identify the source of the contamination, the hospitals will look in the area which showed the most infections for the timeframe April 18—March 18. Random patients from the hospitals are given a questionnaire asking about possible places where they might have been infected.

After conducting the interviews and collecting the research, the following data stood out from the rest:

3% of the people who were showing symptoms ate in the same restaurant

62% of the people who were showing symptoms went to the same shopping center

85% of the people who were showing symptoms drank city water

86% of the people who were showing symptoms commuted to work

69% of the people who were showing symptoms shopped at the same supermarket (Water Spout Supermarket)

15% of the people who were showing symptoms bought deli products in the same supermarket

19% of the people who were showing symptoms bought bread in the same supermarket

8% of the people who were showing symptoms bought alcoholic products at the same supermarket

65% of the people who were showing symptoms bought vegetables at the same supermarket

61% of the people who were showing symptoms bought green bell peppers