A new physician, infection control nurse, or healthcare facility may more consistently report cases, when in fact there has been no change in the actual occurrence of the disease. An intermittent common-source epidemic (in which exposure to the causative agent is sporadic over time) usually produces an irregularly jagged epidemic curve reflecting the intermittence and duration of exposure and the number of persons exposed. The expected number is usually the number from the previous few weeks or months, or from a comparable period during the previous few years. Therefore, confidentiality the responsibility to protect a patients private information is critical in TB control and many other situations.(50). London: Humphrey Milford: Oxford U Press, 1936. Moreover, the healthcare worker may lose the trust of the patient, which can affect adherence to TB treatment. The incubation period for hepatitis A ranges from 15 to 50 days (roughly 2 to 7 weeks), with an average incubation period of 2830 days (roughly one month). N Engl J Med 1977;297:118997. Some 31% say they have heard a lot about the government surveillance programs and another 56% say they had heard a little. An epidemic curve that has a steep upslope and a more gradual down slope (a so-called log-normal curve) is characteristic of a point-source epidemic in which persons are exposed to the same source over a relative brief period. If you have been invited to participate but do not work for the local health agency, are you expected to lead the investigation, provide consultation to the local staff who will conduct the investigation, or simply lend a hand to the local staff? Anger. A large community outbreak of salmonellosis caused by intentional contamination of restaurant salad bars. Some epidemiologists apply the term epidemic to situations involving larger numbers of people over a wide geographic area. Return to text. (40) The following table shows the number of case-patients and controls who worked in Building X, near a recently excavated site. fdoov 7khvh vwhsv pd\ khos lq ilhoglqj lqyhvwljdwruv idvwhu dqg lqlwldwlqj dq lqyhvwljdwlrq ,w lv dovr yhu\ grhv wkh /+' kdyh wkh phdqv wr surshuo\ frqgxfw wkh lqyhvwljdwlrq ru lv wkhuh d qhhg wr vhhn rxwvlgh dvvlvwdqfh" ,i dq rxweuhdn lqyhvwljdwlrq uhtxluhv dgglwlrqdo uhvrxufhv .'3+ This is because at each step in the surveillance process, some individuals or patients are missed. Return to text. 5. When they visited the dairy, they quickly recognized that the dairy was inadvertently adding far more than the recommended dose of vitamin D to the milk. For example, in an outbreak of listeriosis in 2002 caused by contaminated sliceable turkey deli meat, announcements in the media alerted the public to avoid the implicated product and instructed them to see a physician if they developed symptoms compatible with the disease in question.(27). All outliers are worth examining carefully because if they are part of the outbreak, they may have an easily identifiable exposure that may point directly to the source. Many clients simply want to give you the subjects name, age and address and leave it at that. Public health dispatch: outbreak of listeriosis northeastern United States, 2002. This part includes the STEPS Instrument as well as the question-by-question guide, the show cards, and . These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. Patients from the same physician practice or hospital who do not have the disease in question. Anthrax outbreak averted: public health response to a contaminated envelope on Capital HillWashington, DC, 2001. Figure 6.4 Number of Cases of Acute Hemorrhagic Conjunctivitis, By Month and Week of Report Puerto Rico, August 7October 30, 2003. On the other hand, these outlying cases sometimes represent miscoded or erroneous data. Are intervention measures working? Is the number of new cases slowing down or, better yet, stopping? Including more than four controls per case is rarely worth the effort in terms of increasing the statistical power of your investigation. In addition, operational and logistical details are important. We should carefully scrutinize any surveillance that threatens our intellectual privacy. Only occasionally do public health officials decide to conduct a field investigation before confirming an increase in cases and verifying the diagnosis. Introduction: Malaria is a life-threatening disease ocuring mainly in developing countries. Investigators of a school-based gastroenteritis outbreak might describe occurrence by grade or classroom, and by student versus teacher or other staff. An early case may represent a background or unrelated case, a source of the epidemic, or a person who was exposed earlier than most of the cases (for example, the cook who tasted a dish hours before bringing it to the big picnic). There appeared to be no clustering by either residence or worksite, and no connection with exposure to the towns cooling towers. The opposite can also occur a p-value less than 0.05 can actually be a chance finding rather than the true explanation of the outbreak. Source: Jernigan DB, Raghunathan PL, Bell BP, Brechner R, Bresnitz EA, Butler JC, et al. Description: Map showing the counties of Wisconsin. The World Health Organization (WHO) defines public health surveillance as the "continuous, systematic collection, analysis and interpretation of health-related data needed for the planning, implementation, and evaluation of public health practice. The most common statistical test for data in a two-by-two table from an outbreak is the chi-square test. Return to text. Surveillance is the monitoring of behavior, many activities, or information for the purpose of information gathering, influencing, managing or directing. Adapted from: Tan C. A preventable outbreak of pneumococcal pneumonia among unvaccinated nursing home residents in New Jersey during 2001. In contrast to outbreak and epidemic, a cluster is an aggregation of cases in a given area over a particular period without regard to whether the number of cases is more than expected. Sometimes, health agencies respond to small numbers of cases, or even a single case of disease, that may not exceed the expected or usual number of cases. Return to text. The need for communicating with the public health and clinical community has long been acknowledged, but the need for communicating quickly and effectively with elected officials and the public became obvious during the epidemics of West Nile Virus encephalitis, SARS, and anthrax. Steps in carrying out surveillance (go to Outline) But surveillance involves carrying out many integrated steps by many people: Reporting Someone has to record the data. Figure 6.7 Desk Locations of Persons with Nasal Swabs Positive for Bacillus anthracis, Hart Building Washington, DC, 2001. This step is critical for several reasons. When the attack rate for the exposed group is the same as the attack rate for the unexposed group, the relative risk is equal to 1.0, and the exposure is said not to be associated with disease. In a similar fashion, if the time of exposure and the times of onset of illness are known but the cause has not yet been identified, the incubation period can be estimated from the epidemic curve. Tan C. A preventable outbreak of pneumococcal pneumonia among unvaccinated nursing home residents New Jersey, 2001. Solna, Sweden: Smittskyddsinstitutet [updated 2004 Sep 27; cited 2006 Sep 22]. Investigators then abstract selected critical items onto a form called a line listing (See Lesson 2 for more information on line listings. For example, a child with measles in a community with other susceptible children may prompt a vaccination campaign before an investigation of how that child became infected. The investigators asked case-patients and controls how much time they spent in the store and where they went in the store. After characterizing an outbreak by time, place, and person, it is useful to summarize what you know. It is an axiom of field epidemiology that if you cannot generate good hypotheses (for example, by talking to some case-patients or local staff and examining the descriptive epidemiology and outliers), then proceeding to analytic epidemiology, such as a case-control study, is likely to be a waste of time. : Yes; Hospital Alerted: Yes; Lab Results: WB IgM+, WB IgG+;Comments: Erythema migrans, arthritis, fatigue, sweats, fever; Physician Reporting: Dr. Farr; Phone: 555-1313; Date of Report: 11/24/06. Some outbreak investigations require no special equipment while an investigation of SARS or Ebola hemorrhagic fever may require personal protective equipment such as masks, gowns, and gloves. How would you interpret your results? In the example above, since the investigators did not know how many community residents did or did not shop at Grocery Store A, they could not calculate attack rates or a risk ratio. Referring to Table 6.10, a chi-square of 13.02 corresponds to a p-value less than 0.001. To identify the likely period of exposure from an epidemic curve of an apparent point source epidemic: Ideally, the two dates will be similar, and represent the probable period of exposure. Here, as in other areas of epidemiology, the observed is compared with the expected. Attack rate (risk)in exposed groupAttack rate (risk)in unexposed group. New Engl J Med 1992;326:11737. Investigators conducted a case-control study of histoplasmosis among industrial plant workers in Nebraska. Finally, recall that one reason to investigate outbreaks is research. Why are some groups with particular age, sex, or other person characteristics at greater risk than other groups with different person characteristics? 2. Single case of disease caused by an uncommon agent (e.g., glanders, smallpox, viral hemorrhagic fever, inhalational or cutaneous anthrax) without adequate epidemiologic explanation, Unusual, atypical, genetically engineered, or antiquated strain of an agent (or antibiotic-resistance pattern), Higher morbidity and mortality in association with a common disease or syndrome or failure of such patients to respond to usual therapy, Unusual disease presentation (e.g., inhalational anthrax or pneumonic plague), Disease with an unusual geographic or seasonal distribution (e.g., tularemia in a non-endemic area, influenza in the summer), Stable endemic disease with an unexplained increase in incidence (e.g., tularemia, plague), Atypical disease transmission through aerosols, food, or water, in a mode suggesting deliberate sabotage (i.e., no other physical explanation), No illness in persons who are not exposed to common ventilation systems (have separate closed ventilation systems) when illness is seen in persons in close proximity who have a common ventilation system, Several unusual or unexplained diseases coexisting in the same patient without any other explanation, Unusual illness that affects a large, disparate population (e.g., respiratory disease in a large population may suggest exposure to an inhalational pathogen or chemical agent), Illness that is unusual (or atypical) for a given population or age group (e.g., outbreak of measles-like rash in adults), Unusual pattern of death or illness among animals (which may be unexplained or attributed to an agent of bioterrorism) that precedes or accompanies illness or death in humans, Unusual pattern of death or illness among humans (which may be unexplained or attributed to an agent of bioterrorism) that precedes or accompanies illness or death in animals, Ill persons who seek treatment at about the same time (point source with compressed epidemic curve), Similar genetic type among agents isolated from temporally or spatially distinct sources, Simultaneous clusters of similar illness in noncontiguous areas, domestic or foreign, Large number of cases of unexplained diseases or deaths. First, consider what you know about the disease itself: What is the agents usual reservoir? Furthermore, the well was found to be close to the manure pits and a septic tank for the workers dormitory. Recover. Adapted from: European Programme for Intervention Epidemiology Training [Internet]. This is an online version of a printed textbook. The plan should include how often and when to have conference calls with involved agencies, who will be the designated spokesperson, who will prepare health alerts and press releases, and the like. If you need to go back and make any changes, you can always do so by going to our Privacy Policy page. The 5 Whys and/or 8 Disciplines of Problem-Solving (8D) approaches are good root-cause analysis techniques that can help them work together on crafting a good problem statement, identifying the root cause/s, and brainstorming on appropriate solutions to address non-conformance. Do they know anyone else with the disease? : Yes; Hospital Alerted: Yes; Lab Results: WB IgM+; Comments: Erythema migrans; fatigue, sweats, chills; Physician Reporting: Dr. Thus, a line listing contains key information on every case and can be scanned and updated as necessary. Nonetheless, many investigators attempt to enroll such population-based controls through dialing of random telephone numbers in the community or through a household survey. Preparedness and readiness go hand in hand as organizations and communities prepare for disaster. Similarly, prophylactic use of antimalarial drugs, recommended for visitors to malaria-endemic areas, does not prevent exposure through mosquito bites but does prevent infection from taking root. Centers for Disease Control and Prevention. The chi-square test works well if the number of people in the study is greater than about 30. Research for a new drug begins in the laboratory. Or are new cases continuing to occur? The illness was given the name eosinophilia-myalgia syndrome. Last JM. MMWR 2002;51:9501. Baseline surveillance data is a useful resource for making . You should also take care of personal matters before you leave, especially if the investigation is likely to be lengthy. : Yes; Hospital Alerted: YesColumbia Medical Ctr; Admission Date: 9/18/2006; Lab Results: WB IgM+, WB IgG-; Comments: Erythema migrans; Physician Reporting: Dr. Fine; Phone: 555-1951; Date of Report: 11/24/06. Even if the cases turn out to be the same disease, the number of cases may not exceed what the health department normally sees in a comparable time period. For example, in many hospital outbreaks, investigators use an initial study to narrow their focus. N Engl J Med 2001;344:180714. Aha! But every step you take will make you a little bit safer than average. Most of the case-patients were exposed to the item, so that the exposure could explain or account for most, if not all, of the cases. Interruption of direct transmission may be accomplished by isolation of someone with infection, or counseling persons to avoid the specific type of contact associated with transmission.
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