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 Pam Pontones, MA, RM(AAM)
ISDH Epidemiology Resource Center

The main objective of any communicable disease outbreak investigation is to identify the infectious agent and the causative factors in order to control the outbreak and prevent further disease transmission. Thorough investigations can also monitor emerging trends and provide a knowledge base to prevent similar occurrences in the future. Therefore, outbreaks or clusters of unusual disease incidence are reportable to the Indiana State Department of Health (ISDH) [IAC 410 1-2.1]. Outbreak investigations should be a collaborative effort between the local health departments and ISDH. Generally, it is the local health department�s responsibility to notify ISDH of the outbreak and to perform the majority of investigative procedures, while the ISDH role is mainly coordination and consultation. In large or complex outbreak situations, the ISDH may provide direct or on-site assistance.

This narrative describes only those outbreak investigations in which the ISDH Communicable Disease Program (CDP) participated. The ISDH Communicable Disease Program investigated a total of 14 outbreaks in 1999 (Table 1). Two of these involved respiratory agents; the others were foodborne. No waterborne outbreaks were reported in 1999. The Food Protection Program (FPP), in addition to lending valuable expertise and experience during these investigations, also investigates a substantial number of other food-related outbreaks and complaints for which the CDP never becomes involved.

From May 24 to July 17, twenty-two cases of pertussis occurred in Hamilton County. Nine of the cases (41%) were linked to a church in Noblesville. Ages of the church cases ranged from 2 months to 17 years, with four of the cases (44%) under one year of age. Although they occurred within the same time period, the thirteen other cases could not be linked to any of the church cases. The ages of these thirteen cases ranged from one month to 35 years, with one of the cases (8%) under one year of age. Six of the cases were culture confirmed and two were hospitalized. Forty-nine contacts of the cases received antibiotic prophylaxis. Of the fifteen cases � 15 years, nine (60%) had received the recommended doses of vaccine. Pertussis is a highly communicable disease that is most commonly transmitted through airborne contact with respiratory droplets. Up-to-date immunization with pertussis vaccine remains the most effective means to prevent illness.

In June, an outbreak attributed to Mycoplasma pneumoniae occurred at a state psychiatric institution in Vanderburgh County. At least 36 residents and 39 staff were affected. Ages of the case residents ranged from 19 to 87 years. Nine of the residents tested positive for M. pneumoniae by PCR testing performed by CDC, and no viral agents were identified. On August 16, four CDC employees traveled to Vanderburgh County to define the scope of the outbreak and assist with control efforts. One objective was to conduct a study of azithromycin prophylaxis in employees to determine if mycoplasmal carriage and illness could be reduced. Mycoplasma infection commonly presents as a febrile lower respiratory infection and is primarily transmitted by direct contact with infectious droplets or by airborne spread.

In July, an outbreak of Salmonella serotype heidelberg was reported in Martin County. Thirteen cases were identified, all of whom had eaten at a local Martin County restaurant, and nine (69%) were culture confirmed for S. heidelberg. No food vehicle was confirmed due since leftover food samples were not available for testing. However, all cases ate tapioca pudding, while no controls did. Food poisoning due to this agent is usually attributed to inadequate cooking, particularly of poultry and eggs, temperature abuse, and cross-contamination of foods.

On September 19, an outbreak occurred among extended family member gathered at a Steuben County residence for dinner. Four cases were identified, and one tested positive for Shigella sonnei. No food vehicle tested positive for Shigella sonnei. However, all cases ate potato salad, while only 2 of 7 controls did. One of the family members who prepared the potato salad became ill that evening. Foodborne illness due to this agent is usually attributed to an infected person who does not adequately wash hands after using the restroom and then prepares food that is served raw or handled extensively after cooking.

In October, an outbreak attributed to Staphylococcus aureus toxin occurred at an office party in Tippecanoe County. Eight cases were identified. A case-control study did not identify a specific food vehicle, but all cases reported eating ham brought to the party. Samples of leftover ham contained high levels of S. aureus as well as elevated aerobic plate counts, which indicated temperature abuse and mishandling. In November, at least twenty-two people became ill with gastroenteritis following a church pitch-in dinner in Ripley County. No food vehicle was identified, and no food samples were available for testing. However, the epidemiologic features and clinical syndrome was most compatible with S. aureus. Staphylococcal food poisoning is usually attributed to time and temperature abuse.

Five suspected viral outbreaks occurred all over the state. In September, an outbreak occurred in Marion County that became the largest foodborne outbreak in state history. In most cases, there was a background of illness in food handlers prior to the outbreak. Foodborne viral outbreaks usually occur when an infected person handles raw foods (salads, vegetables, etc.) or ready-to-eat foods (sliced luncheon meats, rolls, etc.) without thoroughly washing hands after using the restroom. For the first time, laboratory testing of patient samples for viral foodborne agents became available.

No specific agent was identified in two foodborne outbreaks due to limited exposure data and inconclusive laboratory results.

Based on our experiences in disease investigation, the Communicable Disease Division and Food Protection Program make the following recommendations to local health departments for efficient and scientifically sound disease investigations:

• Ensure that everyone involved in the process is working together. This may involve initial and even daily meetings among environmental and nursing staffs.
• Maintain supplies for outbreak investigations. Inventory supplies to make sure you are equipped to investigate outbreaks. If the outbreak is foodborne, containers for collecting stool samples specific for bacterial and viral pathogens (7A) should be readily available. Be sure to check the expiration dates on the containers. New containers can be ordered or expired ones replaced by calling the ISDH Containers Section at (317) 233-8104.
• If an outbreak is suspected, contact ISDH as soon as possible. Gather basic information about the outbreak beforehand. This includes:
• Type of event, location, date, number of meal(s) served and time of meal(s)
• Source of food served (caterer, home, etc.) and contact person for the source
• Number of exposed persons
• Number of known ill persons
• Range and times of illness onset
• Main symptoms
• Contact person for ill persons and phone number, if possible
• Menu of all food and beverage items served
• Availability of clinical and food samples

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