plying Epidemiology

HCA 415: Community and Public Health

Online

Epidemiological Case #1: Norovirus in Vermont

PART I

On the morning of February 5 th , the mother of a young child called the Vermont Department of

Health (VDH) to report a possible foodborne outbreak. The woman’s child, age 5 years, and two

neighborhood children, ages 7 and 10 years, had become ill with vomiting and diarrhea within 12

hours of each other. The child aged 5-years had become so sick that her mother had taken her to the

emergency department at the local hospital.

Question 1: What questions (or types of questions) would you ask the mother to help

determine the seriousness of this problem and the steps needed to explore the problem further?

The mother reported that her child initially complained of nausea around 10:00 a.m. on Monday,

February 2 nd

. The nausea was followed by vomiting and multiple episodes of diarrhea. The child was

unable to eat or drink anything without vomiting. Toward evening, the child became listless. The

woman took the child to the emergency department where she was noted to be dehydrated and that

she had a fever. Stool and blood specimens were collected, and the child was treated with

intravenous fluids and released.

The mother called the emergency department the following day to receive the test results for

her child. A nurse told her that preliminary stool culture results were “negative for the usual

bacteria.” The two neighborhood children had had similar symptoms (i.e., nausea, vomiting,

diarrhea, and fever) but had not become as ill as the woman’s child. Their symptoms started a few

hours earlier than her child’s. Both had returned to school the day after becoming ill.

The three children usually did not play together but had attended a birthday party on the

morning of Sunday, February 1 st . The mother was concerned about homemade ice cream that was

served at the party because she had heard it had been prepared using raw eggs.

Question 2: What etiologic agents are consistent with the illness among the children?

After confirming the mother’s information with the emergency department physician, VDH staff

called the mother who had organized the February 1 st birthday party. The woman reported that her

own child was well (except for a cold). Other parents had called her, however, saying that their

HCA 415: Community and Public Health

Online

children had become ill with vomiting and diarrhea. The woman reported that her son’s birthday

party had occurred at a private indoor swim club in Essex, Vermont, close to Burlington.

Approximately 30 children and adults were in attendance. The children ranged in age from 5 to 10

years. Not all of the children attended the same school.

Cake, ice cream, and canned drinks had been served at the party. All refreshments had been

commercially prepared. The ice cream had not contained raw eggs. The majority of children had

played in the pool at the swim club before presents were opened and cake and ice cream were

served. Two children who later became ill had left the party before cake and ice cream were served

to attend another birthday party. The mother provided a list of party attendees, indicating which ones

she knew had been ill, and their telephone numbers. She also provided the name and telephone

number for the swim club manager.

Question 3: On the basis of the information provided so far, what actions would you take?

Whom would you contact? What additional information would you be interested in collecting?

VDH investigators notified the district health department of the problem and then contacted the

manager of the private swim club. The manager stated that he was dealing with a “problem” and

refused to talk with health department investigators. He suggested that they leave their telephone

number and he would call them back if he had time.

Question 4: How would you approach the swim club manager to gain his cooperation?

After VDH investigators stated the reason for their call and reassured the swim club manager that the

health department needed to investigate the reported illnesses so that the source could be found and

actions could be taken to prevent others from becoming ill, the manager spoke with investigators.

The manager had not heard about the illnesses associated with the February 1 st birthday party, but

had received reports of illness among other persons who had used the pool during the weekend.

Rumors were circulating that participants in the infant-mother swim class (that last met on Saturday,

January 31 st ) were sick with “stomach flu.”

The manager provided VDH investigators with the names and contact information for persons

who had complained to him about being ill and for members of the infant-mother swim class.

VDH investigators, with the assistance of district health department staff, contacted households of

persons who had visited the swim club and reported illness since January 27 th to VDH, the mother

organizing the February 1 st birthday party, or the swim club manager. Investigators asked about

HCA 415: Community and Public Health

Online

specific symptoms, the date of illness onset, and the most recent date the ill person had visited the

swim club.

On the basis of these calls, 21 individuals were identified as having attended the swim club and

having reported being ill (Table 1). Signs and symptoms included vomiting (90%), nausea (81%),

abdominal cramps (67%), diarrhea (48%), fever (48%), and headache (43%). Symptoms began a

median of 30 hours (range: 8−62 hours) after visiting the swim club.

Table 1. Line list of persons becoming ill after a visit to the private swim club, Essex, Vermont,

January 27 th

− February 1 st .

Patient No.

Age

Sex

Signs and Symptoms*

Examined by a doctor

Date of symptom onset

Date of exposure to the pool

1 5 yrs F V, D, N, C, F, H Yes 2/2 2/1 (morning)

2 7 yrs M V, D, N, C, H 2/1 2/1 (morning)

3 10 yrs M V, D, N, C, H 2/2 2/1 (morning)

4 5 mos F V, F 2/1 1/31 (morning)

5 1 yrs M V, D Yes 1/31 1/31 (morning)

6 (mother of #5) 31 yrs F D, N, C, F 2/1 1/31 (morning)

7 7 yrs M V, N, C, H 2/1 2/1 (morning)

8 11 yrs F V, N, C, H 2/2 2/1 (afternoon)

9 65 yrs M D, N, C, H 2/2 2/1 (morning)

10 18 mos F V, D, N, F 2/1 1/31 (morning)

11 11 mos F V, D 2/2 1/31 (morning)

12 7 yrs M V, D, N, C, F 2/3 2/1 (morning)

13 61 yrs F V, D, N, C, F Yes 2/2 2/1 (morning)

14 2 yrs M V, N, F 2/2 1/31 (afternoon)

15 5 yrs M V, N, H 2/2 2/1 (morning)

16 8 yrs F V, N, C, H 2/3 2/1 (morning)

17 12 yrs F V, N, C, H 2/1 1/31 (afternoon)

18 10 yrs F V, N, C, F 2/2 2/1 (morning)

19 8 mos M V, F Yes 2/1 1/31 (morning)

20 (mother of #19)

22 yrs F V, N, C 2/3 1/31 (morning)

21 12 yrs F V, N, C, F 2/2 1/31 (afternoon)

HCA 415: Community and Public Health

Online

*V = vomiting; D = diarrhea (defined as 3 or more loose stools in a 24-hour period); F = fever; N = nausea; C =

abdominal cramps; and H = headache.

Question 5: Summarize the descriptive epidemiology of cases. Do signs and symptoms among

patients support your earlier suspicions about the causative agent? Were cases clustered by

selected demographic characteristics? What was the time course of the outbreak?

During the calls, multiple parents, who had been at the pool on January 31 noted that the water in the

pool had been cloudy. One parent had reported the pool’s condition to the lifeguard and was told that

the cloudiness resulted from chemicals added to the water. The parent later saw another swim club

staff member collecting water from the pool for testing. No one reported having seen a fecal incident

or vomiting while they were at the pool.

On the basis of the initial findings, VDH investigators believed that the gastrointestinal illness

was consistent with Norovirus infection. They hypothesized that the virus was spread by exposure to

the pool at the private swim club on Saturday, January 31, or Sunday, February 1. The district health

department arranged collection of stool specimens from 10 patients for norovirus testing at the

Centers for Disease Control and Prevention (CDC), using reverse transcription-polymerase chain

reaction (RT-PCR).

Question 6: What studies or investigations would you undertake to explore the hypothesis that

exposure to the pool at the private swim club was the source of the outbreak?

PART II

Based on this week’s readings and your knowledge of epidemiological concepts address the

following questions:

Which offices need to respond? How would you coordinate a response?

Does the case require an immediate public health response?

Determine what type of emergency is described in the case below. Is this an epidemic,

endemic, pandemic or an isolated incidence?

List categories and examples of questions that should be asked of key informants who report

a suspected outbreak of foodborne disease

Describe the steps for management of fecal incidents in treated recreational water venues.

discuss considerations in working with businesses that might be identified as a possible

source of an outbreak;

HCA 415: Community and Public Health

Online

Discuss considerations in working with businesses that might be identified as a possible

source of an outbreak;

Identify activities that increase a person’s risk for exposure to pathogens in recreational

water;