A hospital has been set up to supply medical and surgical service for the workers and staff at a large oil extraction and processing operation in northern Canada. During early January, several cases of painful sore throat (pharyngitis) are reported in patients who had recently undergone surgical procedures for other reasons at the hospital, and an infection-control problem is suspected. Samples have been taken but they have to be flown to Winnipeg for analysis and will not be available for about a week. As all the patients are workers for the company, and the infections occurred while on the job, you (as the OH&S specialist with some knowledge of epidemiology) are working alongside the HICP (Hospital Infection-Control Practitioner) to investigate the problem. Reports for the entire group of workers for the previous several months show roughly 3 or 4 cases of this type of pharyngitis every month.
1.Plot the time of onset for each person (the “epidemic” curve), using one-day intervals for each day of the month. The histogram should be clearly labelled (title, y and x-axis) and easily read, and should clearly show the time of onset.
2.Next, plot the “elapsed time” curve which shows a time of ‘zero’ for each person’s operation, and the distribution of marks for each person following the operation time (Use the same 1-day intervals). This has the effect of accumulating everyone together relative to their own operation time as if it were the same moment.
3.What does this tell you about the range of the incubation period as well as the median incubation period?
4.Is there evidence of propagation in this outbreak? Why or why not?
5.Does this constitute an “epidemic”? Why or why not?
6.You have asked for the incidence of reports of this type of pharyngitis in the general worker community outside the hospital during January but the cases are very few, and none directly traceable to the hospitalized patients. What statement can you make about clustering in ‘place’?
7.Is there a relationship between gender and illness among the surgical patients during January? [2×2 analysis needed with odds ratios]
8.Is there a relationship between age group (i.e. 16-20, 21-25, etc.) and illness in the surgical patients during January? [2xN analysis needed]
9.Is there a relationship between the type of work and the illness? [2xN analysis needed]
10.What was the overall attack (incidence) rate among the surgical patients during January?
11.Two (patient #17 and #43) developed a urinary tract infection a week after the sore throat, but that may or may not be related to the pharyngitis. Make a symptom profile table showing the percentage of the ill persons who demonstrate the symptoms.Describe the symptom profile.
NOTE: SYMPTOM DATA IS NOT DISPLAYED IN EXCEL FILE: The symptoms are limited to painful sore throat (=all patients), with slight fever (=6 patients), high fever (=3 patients), and earache (=4 patients).
12.Given ALL the evidence you have thus far, and after consulting information sources, try to eliminate as many as possible of the agents on the following list.
Streptococcus Group A
Where you can eliminate any of these agents, explain specifically why it is NOT likely to be that agent. What are you left with?
13.Table 2 shows the surgical team staff who were on duty for each day during the period when infections were occurring. Is there an association between any particular team member present during the operation and the illness? [2×2 tables needed with odds ratios]
14.Write a paragraph summarizing the outbreak for a public health professional journal. Be Clear, Concise, and Accurate.