HEPATITIS A OUTBREAK INVESTIGATION

HEPATITIS A OUTBREAK INVESTIGATION You are a member of the Hepatitis Unit of the Centers for Disease Control and Prevention in Atlanta Georgia. The year is 1968. On May 15th a request to assist in the investigation of an outbreak of infectious Hepatitis A was extended. You learned that 55 cases of infectious hepatitis had been reported to District #2 Health Department in North Trail Michigan. Knowing that between April 1 and May 15 1968 there were 55 cases of Hepatitis A infection reported to the County Health Department could you conclude that this is a problem of epidemic proportion? Justify your response. As members of the Hepatitis Unit you determined that all of the reported hepatitis victims should be interviewed as the first step of the investigation. They will be interviewed in their homes if possible. What questions will you ask?You should identify at least ten questions. What other actions might you take at this time in the investigation while you are at the victims’ homes? What information can you identify from studying daily incidence and the epidemic curve? Make observations about the characteristics of the outbreak in terms of time (i.e Which decade of age had the highest attack rate? And What hypothesis relative to time and person can you make at this point in the investigation?) Make observations about the characteristics of the outbreak in terms of place. What can you conclude from this information about the distribution of disease in terms of time and place? Why is it important to calculate attack rates by age? Using the information calculated about place and person what conclusions can you draw now? From the information in Table 3 what hypothesis can be formed about the source of the infection? Is this type of data alone sufficient to identify a single source? Compare the listed exposures (Table 4). Which source (location) shows the largest differential between well and ill? Explain the high exposure rates to water in both the sick and well groups. What conclusions can you draw about milk possibly being the source of the contamination? Study Figure 2. How do these data aid in the investigation? Review the Case Histories (attached). Are they compatible with the bakery being the source of infection? What would be your next step in the investigation? Does your epidemic curve reveal the incubation period for hepatitis? If so what is it? Does this curve still support a common source of infection? Knowing that infectious hepatitis virus is killed by heat what further investigation would you undertake to confirm the source of the virus? Do you agree with the decision?Justify your response. None of the bakery employees appeared ill. Why were SGPT tests performed? Question 19 Since the epidemic had ended why was it necessary to administer the gamma globulin? How would you evaluate the effectiveness of this control measure? North Trail Public School Saint Luke’s School Grade # in class # ill AR (%) Grade # in class # ill AR (%) K 126 2 1.6 1 128 0 0.0 1 37 1 2.7 2 121 0 0.0 2 41 1 2.4 3 107 0 0.0 3 37 0 0.0 4 106 2 1.9 4 26 0 0.0 5 120 1 0.8 5 30 0 0.0 6 111 1 0.9 6 32 0 0.0 7 110 5 4.5 7 26 0 0.0 8 120 9 7.5 8 21 0 0.0 9 143 12 8.4 10 128 16 12.5 11 112 1 0.9 12 93 2 2.2 Table 2. Attack Rates by Grade and School in Cases of Hepatitis A – Lake County MI Table 3. Exposure History of 41 Hepatitis A Cases Ages 10-19 Lake County MI Food or Water Yes No Unknown % Known Exposed Restaurant A 15 25 1 36.6 Restaurant B 17 23 1 41.5 North Trail Dairy Queen 28 12 1 68.3 Spruce City Dairy Queen 8 32 1 19.5 North Trail Bakery 37 3 1 90.2 North Trail Municipal Water 36 5 0 87.8 Table 4. Comparison of the Exposure History of 41 Cases of Hepatitis A in the 10-19 year old age group with the Exposure History of a Group of 56 Well Household Members in the 10-19 year old age group Lake County MI Hepatitis Cases Number Yes Number No Number Unk % Known Exposure Restaurant A 15 25 1 36.6 Restaurant B 17 23 1 41.5 North Trail DQ 28 12 1 68.3 Spruce City DQ 8 32 1 19.5 North Trail Bakery 37 3 1 90.2 North Trail Water 36 5 0 87.8 Well Household Members Restaurant A 22 31 3 39.3 Restaurant B 15 39 2 26.8 North Trail DQ 39 17 0 69.6 Spruce City DQ 6 50 0 10.7 North Trail Bakery 26 29 1 46.4 North Trail Water 51 4 1 91.1 Figure 2. Percent of Total Persons Patronizing North Trail Bakery by Hour of Sale and Age

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Are 55 cases in excess of normal expectancy? How did you establish whether this is greater than expected?