Conducting Surveillance

Table of Contents

Introduction

Surveillance of foodborne illness provides the framework in which public health officials can act to control and prevent diseases that may be acquired through food.  Surveillance is necessary to determine the occurrence or significant changes in frequency or distribution of cases.  These observations are a continuous process to determine the extent of disease and risk of transmission and to assess the impact prevention and control measures. 

What is surveillance?

Disease surveillance is the regular collection, monitoring and analysis of data for control and prevention of diseases or other conditions. The data may be used to determine baseline levels of disease. Knowing the baseline, one may identify unusual occurrences of disease, such as an increased incidence or abnormal distribution.

The purposes of foodborne illness surveillance are to interrupt transmission of disease to susceptible persons and to reduce morbidity and mortality through:

  • Education,
  • Identification and investigation of outbreaks, and
  • Interpretation of investigative data and dissemination of findings.

Surveillance is often categorized into two types: “active surveillance” and “passive surveillance.”

Active Surveillance 

An active surveillance system is one in which public health officials regularly solicit disease reports.  This is often done by regularly (daily, weekly, bi-weekly) telephoning selected people, generally physicians, infection-control practitioners at hospitals, laboratories, schools, urgent care clinics, etc. and asking if specific diseases have been noted. This type of system has been shown to double the number of reports of some diseases.  Active surveillance also is used during outbreak investigations. 

In active surveillance, the organization receiving information takes direct action in collecting it. This may also occur through review of medical records, laboratory records, interviewing individuals in an outbreak investigation, or screening of high-risk populations.

Passive Surveillance 

A passive surveillance system, such as Iowa’s routine reportable disease system, is one in which reporting is left to individuals (i.e. physicians, infection control practitioners at hospitals, laboratories, or individuals themselves in the case of a foodborne illness complaint, etc.).  It’s the most common routine surveillance system used by the state and local public health agencies.  The two major limitations of this type of system are underreporting and delayed reporting.

Traditional reporting of diseases by healthcare providers and laboratories is considered passive surveillance. This means that the organization receiving the information waits for initial data on a case to be submitted. This usually leads to collection of additional information and the implementation of follow-up activities. An example is a local public health agency receiving a report of E. Coli O157:H7 infection from a healthcare provider or facility.

A sub-category of passive surveillance is “enhanced passive surveillance” in which the organization receiving data works closely with the healthcare providers and laboratories most likely to report a particular disease or group of diseases and sets up systems to increase timeliness and completeness of reporting.

Information You Need to Collect 

Two main categories of information should be collected as part of a foodborne illness surveillance system:  descriptive information and investigational findings

Descriptive Information

First, information is needed regarding the time(s), place(s), and person(s) connected with a possible foodborne illness.  Collecting this descriptive information will help determine whether any related illnesses have been received and whether these illnesses need to be investigated more extensively. When notified of a potential foodborne illness, the following information is needed:

Who, When, What, Where

  • Who became ill and what are the characteristics of this person(s), that is age, sex, occupation?
  • When did the person(s) become ill?
  • What foods, beverages, or meals are suspect and what symptoms are people having?
  • Where did the ill person(s) eat or buy the food and when did they consume them?   

Investigational Findings

A second category of information is collected as an investigation proceeds. It is a crucial component of foodborne illness surveillance because such findings enable public health officials to more clearly understand the causes of foodborne illness, stop any ongoing problems and help prevent future illness.  Findings may include the answers to some of the following questions:

  • What specific food item(s) or ingredient(s) was linked to the illness?
  • What type of contaminant (bacterium, virus, parasite, toxin, chemical) caused the illness?
  • What were factors leading to the contamination, survival, or growth of a contaminant in the implicated food?  How was it prepared, stored, served, etc.? Was the item improperly cooked or stored?  Did a sick food-handler prepare the food?

Methods for Collecting Information

One method of collecting information on a potential foodborne illness is to complete the Preliminary Foodborne Illness Complaint Form when a complaint is received.  Please refer to Chapter 6 Handling Complaints for additional information on use of the Preliminary Foodborne Illness Complaint Form.

Another method for collecting information on potential foodborne illness is through routine follow-up of reportable diseases.  Several reportable diseases can be acquired through foods, including laboratory-confirmed Salmonella, Listeria, and E.coli O157:H7 must be reported to public health.  Local public health agencies collect information on these cases and forward the case investigation report forms to the Iowa Department of Public Health (IDPH), Center for Acute Disease Epidemiology (CADE). 

Iowa Reportable Disease Surveillance System

Through reporting, a surveillance system receives a timely and regular flow of information on cases.  As mentioned, some Iowa reportable diseases can be acquired through food.  Most are gastrointestinal, such as Salmonellosis, and, once confirmed, additional information is collected and reported by local public health agencies using the Enteric Disease Follow-up Form.  Several case report forms are available for other reportable diseases that can be foodborne, such as Listeriosis and Trichinosis.  These forms can be found in the Epi Manual under each specific disease. 

When a local agency receives notification of a reportable disease from a healthcare provider, laboratory, or other reporting sources, it should be reported as soon as possible to the IDPH. 

The local public health agency (LPHA) will begin collecting information requested and record it on the Enteric Disease Follow-up Form or other appropriate case reporting form.  Since initial case reports usually contain minimal information, completion of the follow-up form may provide clues for determining a possible or probable means through which a person may have become infected (e.g., a summer cook-out or consumption of home-made ice cream).  To complete the follow-up form, it may be necessary to contact the laboratory or provider to get the information needed to contact the ill person (address, phone numbers, etc.).

Please consider the following when completing an Enteric Disease Follow-up Form:

  1. Accurately record dates and times of onset of illness and symptom information.
  2. Refer to the correct incubation period range for the etiologic agent reported (for example, typically the longest incubation period for Salmonella is three days)
  3. Knowing the incubation period, ask the case about exposure history during one incubation period before the illness started. For example, if the patient had Salmonella, ask about exposures during the period three days before the illness started).
  4. Ask about exposure history, including:
    • Questions about travel history and outdoor activities to identify where the patient became infected. Some diseases are endemic in certain countries.  Some activities, such as swimming in infected water, can expose people to certain illnesses.
    • Questions about animal contact, because some animals carry and transmit enteric diseases to humans. Reptiles, for example, can shed Salmonella in their feces, which can then be transmitted to humans through poor hygiene or food contamination.
    • Questions about water usage, because many agents that cause gastrointestinal illness can be transmitted through water.
  5. Using questions on the form, examine the case’s risk for having either acquired illness from household or child-care contacts or for transmitting the illness to these contacts.
  6. Keep in mind that food handling not only can refer to restaurant employees, but also to healthcare providers, dental employees, food-processing workers, child-care workers and others.
  7. Attach the laboratory report to the follow-up form, keeping a copy of all forms in an appropriate filing system at the local level.
  8. Promptly send the completed follow-up form in envelopes marked “confidential” to:

Iowa Department of Public Health, CADE
Lucas State Office Building, 6th Floor
321 E. 12th St.
Des Moines, IA 50319-0075
Or Fax it to:  515-281-5698 

Reporting Issues: Timeliness, Priorities, and Confidentiality

Reporting and Case Investigation - State versus Local Role  

The Center for Acute Disease Epidemiology (CADE) collaborates with LPHAs in the investigation of communicable disease and the implementation of appropriate control and prevention measures. The guidelines in this manual, as well as other referenced material, form the basis for local public health agency communicable disease reporting, investigation and control.  For foodborne illnesses, local health departments take the primary role in investigating individual cases of reportable disease.

When clusters or outbreaks of illness, potential bioterrorist agents, emerging infections or other serious threats to public health are identified, IDPH will often provide technical assistance to local public health agencies. It may range from medical consulting to direct management of the investigation, to implementation of control and prevention measures, and initiating follow-up activities. In special situations, IDPH may request federal technical assistance from the CDC. (Note: Such requests must be made by IDPH.)

When an institution such as a healthcare facility or school is the site of possible transmission, the infection control staff of the facility or school nurse should be involved in the investigation and the application of control and prevention measures. Ideally, IDPH, LPHA, and the infection control staff (or equivalent) in the affected institution collectively make decisions about control measures. However, IDPH and LPHA working together have ultimate authority.

Timeliness 

All cases of diseases reportable to IDPH are reported to CADE using an official case report form. Certain diseases should be immediately reported to CADE by phone when a suspect or confirmed case is identified (refer to disease reporting poster). Diseases that require immediate reporting should be prioritized above other case investigations. Also, any disease cluster or suspected cluster or outbreak should be reported immediately and prioritized accordingly. After the investigation, the local public health agency can follow up with the official case report form(s).  All diseases not categorized as “immediate” should be reported and investigated within a week, and a completed case report form with appropriate laboratory test confirmation (if applicable for the disease) should be submitted.

Note: Local public health agencies are responsible for residents of their county.  Reports of illness received for residents of other cities/towns outside the county should be forwarded to CADE and CADE will notify the appropriate local public health agency.

Priorities

The importance of timely reporting cannot be overemphasized.  For example, if a local health authority holds reports of Salmonella and only submits them once a month, a potential outbreak occurring across county lines may go unnoticed and uncontrolled.

CADE has an epidemiologist available during normal business hours (515) 242-5935 or (800) 362-2736 to answer questions about case investigation and control measures.  Information about reporting requirements is available during normal business hours at (515) 281-6493.  For disease reporting, please call the Disease Reporting Hotline at 1-800-362-2736.  An epidemiologist is also available via beeper during non-work hours and weekends for emergency situations e.g., if you receive several complaints and are concerned about a potential foodborne illness outbreak.  All calls are returned promptly (1-800-362-2736).

Examples of top priorities include:

  • A cluster of illness potentially connected with a specific individual or facility;
  • Foodborne illness in a food handler or household contact of a food handler;
  • Foodborne illness in a healthcare provider or household contact of a healthcare provider;
  • Foodborne illness in a child-care provider, household contact of a child-care provider or a child in child care;
  • Indications of adulterated or contaminated food presenting an imminent danger;
  • One or more botulism cases;
  • Hepatitis A in a food handler.

Note: If you are unsure about which investigations to do first, or need technical assistance, contact the epidemiologist on-call at (800) 362-2736.

Confidentiality

Confidentiality is a legal requirement. The information that public health officials collect is often personal or specific to a company. Success and cooperation from those involved lies in protecting an individual’s or company’s right to privacy. It is important to realize that it is not just the investigator who needs to be concerned about confidentiality. Clerical staff, administrative staff, interns and local public health agency members who may be aware of personal information on a case should all be familiar with and mindful of the basic tenets of maintaining confidentiality. Only people who have a “need to know” should have access to sensitive records. During and after an investigation, only those directly involved in interviewing a case or contacts and/or those directly involved in follow-up activities to control the spread of the disease fall into the category of those who “need to know.” This category would normally not include general administrators, town officials, elected officials and others involved in town government not directly providing disease control. People assisting in general education of the public also have no need to know personally identifying information about a case.

If you are unsure about whether it is appropriate to release information, do not release it!  Check with a supervisor, the municipal attorney or legal advisor, or contact the Center for Acute Disease Epidemiology at (515) 242-5935 or (800) 362-2736 for advice.  Make sure information is released only to people who are authorized to receive it. Do not be pressured into a hasty decision. Do not confirm a case unless you are certain it is appropriate to release that information. Discussing a case or outbreak in a meeting that is open to the public is almost never allowable.  Even confirming there is an outbreak can sometimes allow confidential information to be surmised.  If you are unsure about who is requesting information, obtain confirmation of the requestor’s identity before releasing information i.e., a signed consent form with documented identification such as a driver’s license; for guardians, documentation of guardianship. Inappropriate release of data could pose a liability threat to your agency and/or municipality and possibly endanger affected individuals.

It is important to know that information may be shared between local public health officials and healthcare providers and the IDPH during public health investigations and control activities. However, even in these instances, the “need to know” rule applies. Information on individual cases may be obtained from the IDPH Center for Acute Disease Epidemiology (CADE) only by the responsible representative of a local public health authority involved in an investigation of the case, the person who is the case, the physician involved, or the patient’s guardian or designee (with written informed consent).  Copies of outbreak reports with identifiable information cannot be released, except to those directly involved in the investigation.  Copies of the de-identified outbreak report may be requested from CADE. Interested persons should contact CADE for the proper procedure.

IDPH strongly encourages local public health agencies to acquire a secure fax machine for use of people involved in communicable disease reporting, investigation and control. It should be located in a secure area where disease-control staff work and should not be accessible to the public. Sharing of a fax machine by communicable disease-control staff and personnel in town or county government presents a risk for breach of confidentiality.  Case reports and files on an outbreak investigation should not be left in the open and should, ideally, be placed in a drawer or cabinet when not in use.

It is important to recognize the types of information that may allow identification of a case or company.  This may change with each situation. For example, demographic information, such as age, race, sex, or zip code, may or may not be able to be released depending on factors such as how large the outbreak is and whether it can be traced back to an individual case.  The rule of thumb is that if the information that is released can identify an individual or company or be traced back to an individual case the information should not be released.

Local and state public health authorities have investigated cases of infectious disease and collected sensitive information for more than 100 years. These efforts would not be as successful if all personnel did not uphold the public’s trust by maintaining strict confidentiality.

Important Points on Confidentiality

  • Everyone with access to case information is required to maintain confidentiality.
  • Confidential information can be released only to those who “need to know.”
  • Be certain of the identity of the person to whom you release confidential information. Insist on confirmation of identity e.g. copy of driver’s license, if unsure.
  • Maintain confidentiality during reporting. When mailing case report forms to IDPH, stamp envelopes “CONFIDENTIAL.” If reporting by fax, be certain that the receiving number is a confidential fax; e.g., (515) 281-5698 is the number of the Center for Acute Disease Epidemiology, Surveillance Program confidential fax. When receiving information by fax to your office, confidentiality also must be maintained.
  • Identifying information from case report forms and other forms cannot be released without the patient’s signed consent, except to those directly involved in case investigation, control and prevention who have a “need to know.” 

Recently, there has been concern about medical record disclosure for public health purposes in light of the recently enacted Health Insurance Portability and Accountability Act (HIPAA) act.  The HIPAA Privacy Rule states that a covered entity can, without individual authorization, disclose to a public health authority private information for the purpose of preventing and controlling disease, injury, or disability, including but not limited to, the reporting of disease, injury, or vital event and conducting public health surveillance, investigations, and interventions. (45 CFR 164.512(b) (1)(i)).

Reporting by Clinicians and Laboratories

Clinicians 

Throughout the country, reporting of diseases by clinicians is variable. Clinicians are more likely to report diseases with high mortality or those spotlighted in local and national media.  Some strategies to increase reporting by clinicians include:

  • Education on the importance of reporting;
  • Initiating appropriate mechanisms for reporting;
  • Identification of professional or support staff who work with clinicians and who are able to take the responsibility for reporting of clinician-diagnosed reportable disease;
  • Prioritization of reportable diseases that pose a more serious risk to public health.

Note:  LPHA having difficulty obtaining information from clinicians should contact CADE at (800) 362-2736 for assistance. Also, sample letters outlining the roles and responsibilities of the local public health agency for distribution to healthcare providers and patients are available in disease specific chapters.

An important strategy to improve reporting by healthcare providers is to develop better working relationships with those in your area through education, distribution of reports on public health activities and disease data, and by asking for their participation in timely public health initiatives. This includes such things pandemic influenza planning, or a bioterrorist response and/or surveillance plan for emerging infections.

Healthcare providers do not always inform patients that a disease is reportable to local or state health departments. This may lead to a patients’ distress when they are contacted for an investigation. Healthcare provider education on this issue is a good strategy for local public health agencies, who should determine when test results and diagnoses were communicated to the patient.  It is usually best to begin an investigation by contacting the reporting clinician.

Laboratory

Laboratory reports are often sent directly to IDPH.  This has led to more timely disease reporting. IDPH sends the results to local health agencies for follow-up. Some laboratories batch their test results and submit them periodically, potentially leading to long delays in receipt and identification or confirmation of cases. IDPH is working to eliminate this practice through laboratory education and implementation of electronic laboratory-data transmission.

Current laboratory systems often are not equipped to collect much of the information needed, nor are they linked directly to clinical/patient information systems. As hospital and laboratory databases become more integrated, better demographic information will become available. IDPH currently attempts to gather additional information when patient information is too limited to allow local public health agency follow-up.  If information on healthcare providers who order tests is available, it is best to contact them before contacting the patient to ensure that the case already knows the results of the diagnosis.

Using the Information Collected

To use surveillance information to its full potential, it must be collected and stored accurately and consistently.  Information about possible foodborne illness is collected by two principal methods:  1) Using the Iowa Reportable Disease Surveillance System by completing the case investigation forms for reportable diseases, and 2). Completing the Preliminary Foodborne Illness Complaint Form.  Below is an explanation of ways foodborne illness surveillance information can obtained from each of these methods. 

1.  Using the Iowa Reportable Disease Surveillance System

As part of the case investigation form for diseases caused by potential foodborne pathogens (such as salmonellosis), an appropriate person completes a case investigation report form, which is sent to CADE.  The case’s answers to exposure history may reveal that food was a possible or probable source of the infection.

Case investigation report forms are entered into a large computer database.  Diseases are routinely analyzed for trends.  Occasionally, more cases of a certain disease are reported than would be expected or they have a unique distribution.  In these situations, CADE attempts to determine similarities among the cases, and determine if an outbreak is occurring.  It is clear that reportable disease follow-up at the local level is critical for identifying widespread clusters of foodborne or other illness. 

2.  Preliminary Foodborne Illness Complaint Form

Perhaps the most important reason for using the Preliminary Foodborne Illness Complaint Form  is that it allows local and state public health officials to “speak the same language” on foodborne illness.  Standardized data shared between agencies will be more easily interpreted, providing the opportunity for more rapid responses.

When a complaint is received, descriptive information is requested first from the complainant(s).  Later, any investigational findings can be added to the worksheet.  By consistent and accurate recording and storage of these data, the public health official is maintaining a foodborne illness surveillance system.  Data can be reviewed or analyzed for different purposes, including answering the following questions:

  1. How many complaints about possible foodborne illness were received during defined periods?  How many persons were ill during those periods?
  2. Do the number and/or nature of the complaints appear to be changing over time?
  3. Have certain food establishments or food items been associated with an increase in complaints?
  4. Can you identify links among complaints (using the descriptive information), possibly indicating a more widespread cluster of foodborne illness?
  5. Of the complaints received during a defined period, how many were investigated?
  6. Do certain investigational findings (for instance, certain contributing factors) appear to be related to particular types of establishments or foods?

By routinely examining the data, answers to these and other questions on foodborne illness in the community will emerge.  Such answers will help guide policy making, directing resources to commonly identified problems and identifying potential outbreaks of foodborne illness.

Limitations of Data

Under-Reporting and Incomplete Data 

Because most surveillance systems are based on passive reporting of diseases by healthcare providers, under-reporting is inevitable. It is estimated that, depending on the disease, only 5 percent to 80 percent of cases are reported. For example, foodborne illness is often underreported because people with disease do not consult a healthcare provider, or a diagnosis of “gastrointestinal illness” is made and treated without any diagnostic tests that might identify the pathogen. Even with incomplete information, it is often possible to detect key trends and/or sources of infection. For diseases that occur less frequently, the need for completeness is more important. Each case must be treated as a “key” event.

Lack of Representativeness of Reported Cases

Health conditions are not reported randomly. For example, illnesses in a healthcare facility are reported more frequently than those diagnosed in outpatient care. A provider is more likely to report a case of hepatitis A if the patient is ill than if the patient has few or no symptoms. Reporting bias can distort interpretation of disease data. 

Changing/Evolving Case Definitions

Practitioners use a variety of case definitions for health problems. The more complex the disease syndrome, the greater the difficulty in reaching consensus on a case definition.  With newly emerging diseases and as understanding progresses, case definitions are frequently adjusted to allow greater accuracy of diagnosis. Also, as new diagnostic tests are developed, case definitions sometimes change to incorporate them. Case definitions establish uniform criteria for disease reporting and are not definitive for diagnosis. The use of out-of-date or different case definitions can lead to incomplete or under-reporting of disease.

Bioterrorism

Bioterrorism is the intentional use of disease agents to create fear, disrupt society or cause injuries and/or death. Terrorists’ use of biologic agents may involve acts that are announced or otherwise immediately recognized. Alternatively, and considered more likely, is the silent introduction of a biologic agent into the population that could take days to weeks before illness becomes apparent.

Because some diseases caused by bioterrorism may initially resemble common infectious diseases, the detection of a bioterrorist event could be difficult.  Local health departments should immediately notify the epidemiologist on-call at the Center for Acute Disease Epidemiology at (866) 834-9671 if any of the following are noticed:

  • A cluster of illness that is unexplained after preliminary investigation;
  • One or more cases of disease in a community in which the disease does not normally occur;
  • Illness in an unusual geographic distribution e.g., patients all residing in one area possibly, downwind of a point-location or in an unusual population or e.g., serious pneumonia among young adults;
  • Identification of a category A bioterrorism agent, such as anthrax, even if the situation is not alarming.

Communities will lead the response to a bioterrorist event, or to any infectious disease emergency. Planning and communication are extremely important and will be most effective if a strong partnership among public health, first responders, e.g., fire departments, emergency management, law enforcement and local hospitals, has been developed in advance.  State agencies, such as IDPH and the Department of Homeland Security, are available for consultation or assistance.

Conclusion 

The best surveillance occurs when accurate and timely data is collected and carefully and correctly interpreted. The interpretation should focus on elements that might lead to control and prevention of the condition. Investigators can use surveillance as a basis for appropriate public health actions.  Community baselines can be established, epidemics recognized, preventive strategies applied, and the effects of such actions assessed.