You are examining the relationship between hypertension and myocardial infarction (MI) in your community. In order to do so, you send a questionnaire to the whole population in your community (1000 persons). All 1000 persons responded. The results obtained from that questionnaire are presented below in table.Which of the following statistical tests could best be used to determine whether there is a significant increase in the history of MI among those persons who have hypertension in comparison with those without hypertension?
Answer(s): E
The chi-square test is the most appropriate statistical test to determine whether series of frequencies or proportions are significantly different from each other. It is designed to describe with a single number how much the frequencies in each cell of a box of paired readings differ from the frequency we would expect if there were no relationship between the observed readings. If the observed readings are similar to expected readings, the chi-square will be a small number. If there is a greater difference, the chi- square will be larger. The mathematical equation is:
You are examining the relationship between hypertension and myocardial infarction (MI) in your community. In order to do so, you send a questionnaire to the whole population in your community (1000 persons). All 1000 persons responded. The results obtained from that questionnaire are presented below in table.If we compare the population sample examined with the whole population that responded to the questionnaire, which of the following statements accurately describes the available information?
In a questionnaire relating to history, patients' knowledge as to whether or not they have hypertension or have had an MI might be sufficiently accurate to allow further statistical analysis. The data provided in this questionnaire are not adequate for more detailed statistical analysis. The questionnaire responses rely on memory recall, which at best is questionable, for comparison with an actual examination. Criteria for establishing a diagnosis of MI and, if possible, actual blood pressure readings, as well as a definition of hypertension, are required. The crux of epidemiologic analysis is a detailed criterion for establishing a diagnosis. With this additional information, relevant statistical tests could be applied. In the absence of this information, any further statistical analysis is likely to lead to misleading results.
A 45-year-old male living in a homeless shelter is exposed to TB from a fellow resident. He is found to have a 15 mm of induration on the Mantoux skin test. Which of the following risk factors will increase the man's likelihood of developing active TB subsequent to his infection?
Answer(s): B
Silicosis is considered a risk factor for the development of active TB disease for those who have contracted the infection. HIV infection, malnutrition, IV drug use, alcoholism, leukemia and other cancers, poorly controlled diabetes, severe kidney disease, immune system suppression caused by medications such as drugs to prevent rejection of a transplanted organ, and living in crowded indoor conditions, are also considered risk factors for progression to active disease. Cough variant asthma and bronchitis are not included in this list. COPD can occur as a consequence of chronic TB disease and is not considered one of the risk factors. Siderosis results from accumulation of nonfibrogenic iron oxide particles in the lung and is not considered to predispose to TB.
The causative organism of cholera, Vibrio cholerae, was first isolated by Koch in 1883. There have been seven pandemics of cholera, with the most recent subsiding only in the 1980s. With humans as the usual reservoir, the organism spreads as man travels. Which of the following is the most likely mode of spread?
Answer(s): C
Humans are the usual reservoir of V. cholerae. It tolerates exposure and drying poorly. It survives longest in water, especially if the water is at temperatures of 1823°C (6070°F). It does not spread on infecte d clothing (fomites). Direct person-to-person transmission probably does not occur. Contaminated water is the main source of infection (e.g., frequent exposure to polluted surface water through bathing, food preparation, and utensil washing). Although flies may transport small numbers of vibrios from excreta to food, lack of multiplication makes it unlikely that flies play an important part in transmission. Mosquitoes are not vectors.
A 4-year-old child presents to his pediatrician with a complaint of a mild rash and fevers. His travel history is positive for a camping trip 2 weeks prior. The parents do not recall a tick bite on the child and do not remember if there were ticks in the area. No other members of the family complain of similar symptoms and the child does not attend day care. Physical examination is positive for a temperature of 100.9°F with an erythematous rash noted over the child's trunk. Which of the following factors would significantly increase the possibility that the child has Lyme disease?
Answer(s): D
The principal risk factor for Lyme disease in the United States is residence in an area with high infestation rates of infected ticks. In the coastal northeastern United States, the whitefooted mouse is the most competent vertebrate reservoir of B. burgdorferi, the organism responsible for Lyme disease, with infection rates of up to 80%. Therefore, residence in an area where there is a large population of whitefooted mice will also increase the likelihood ofexposure to Lyme disease. The tick species I. dentatus has maintained cryptic cycles of B. burgdorferi, but it is not considered to be a public health risk because it rarely feeds on humans. Texas is not one of the endemic areas for Lyme disease. Lizards are actually considered to be a zooprophylactic host because they are an incompetent reservoir of B. burgdorferi, and they are also a preferential feeding source for immature stages of the tick. Pesticide spraying is actually protective against tick infestation and therefore will reduce the chances of tick exposure.
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