老师回答如下 轩 To investigate new infection coming to the population of the interest Ａ．Seroincidence: IgM(+) or 4-fold titer rising up or falling down 教授在讲解这个段落的时候，有谈到可用4倍抗体上升或下降来测血清发生率 财 上课有同学问到，为什麽要用4倍？ 教授上课的时候有回答说：如果用2倍，有可能是dilution error..所以至少要4倍 关於这部分我还是不大了解，是不是能请教授再说明一下？谢谢！ Answer: To think as follows: 1. If you get one infection, will you have antibody to that infection by that time? 2. If this person who does NOT have immunosuppression, he/she should get an antibody specific to that infection. Therefore, antibody serotiter should be increased strikingly (eg. >=4-fold). The 2-fold might due to dilution error. 3. We used to dilute antibody as 1:2, 1:4, 1:8, 1:16 etc. 4. Since incidence rate is to measure from time point #1 to time point #2 and that person might have the infection before, you would like to see the quantitative changes of serotiter ONLY　during that time interval. 5. Application when you see a single patient in the future: （a）Be very kind to that patient to explain that you would like to find out which infection she/he might have, you need to collect two serum samples at two time points. One called acute phase and another time point called convalescent phase that you will learn from microbiology course. （b）If you want to know this child has acquired dengue or not, your data showed that child had his serotiter of 1:10 at the acute phase, however the convalescent serotiter showed 1:80 so that this is a NEW case and this child got dengue. You can count this child in the numerator and denominator for obtaining the incidence rate. 6. Application when you see a population (a) You want to know whether an infection of X has come to Taiwan or the community you are interested and at what time it entered to this population. (b) Likely to use to measure magnitude of the infection in children at different age groups so that you will get a feeling when this infection becomes so important since which year. (c) You can compare the risk factors/prevention factors in community A (high incidence rate) vs community B (control group) for further prevention and control Is this clear to you now? . Ｂ．　又有同学问到，为什麽抗体会下降？藉由complement fixation来看抗体的上ꐊ 升或下降，看哪段时间上升或下降。 这教授课堂上也有回答，不过我还是不 是很清楚，是不是能请教授再说明一下？谢谢！ 1. To measure the seroincidence rate related to time point, it would be better to use the antibody with SHORTER DURATION. For example, a person with antibody of yellow fever virus such as complement-fixation antibody positive [frequently used in southern American forest where many arboviruses (arthropod-borne virus) have been circulating there) or IgM antibody positive but it turned to seronegative at 2-3 months later. We will see antibody falling down which also explains that person acquired that infection you are interested around 2-3 months earlier. In other words, we can use complement fixation antibody or IgM antibody both of them with shorter duration to find out this place has yellow fever and differentiate from other virus infections in this forest. 2. Application in patients and populations (a) Have to know which percentage of this antibody is still positive for how long. (b) For example, the study has found that about 80% of dengue-IgM antibody is still positive within 3-6 months. Therefore, you take blood samples and measure the incidence rate of this population. You will know this population had seroincidence of dengue about 3-6 months ago but it cannot explain such an incidence rate about one year ago. Ｃ．教授上课的时候举流行性感冒的例子，提到要用去年血清与今年血清作比较，要用 　 2个time point…但是要同时做？这部分我也不是很清楚，可以麻烦教授在说明一 下吗?谢谢！ 1. Influenza virus is a 8-segmented RNA virus with point mutation of viral genes and antigen we called “antigenic drift” 2. Due to the frequent changes of virus, we would like to know whether the person A has the new infection particularly to the 2005 human flu (HF1) virus strain rather than 2004 human flu virus (HF2). In other words, you would like to know when does this new virus firstly appear? To answer this, we can take A person the two serum samples collected in both 2004 and 2005, then we have both viruses (HF1 and HF2) and run the serological tests of antibody simultaneously. IF this person A has higher serotiter such as 1:1280 to only HF1 but 1:40 to HF2, we know person A acquired the 2005 new virus. In other words, when we check the virus with frequent changes in antigens, we have to run the antibody tests simultaneously to include old year virus and new year virus. This is exactly what we have done for our 1998 enterovirus 71 epidemic paper I mentioned in the class. We had employed the virus strains from old year vs 1998 --

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