流病上課同學提問
老師回答如下
轩 To investigate new infection coming to the population of the interest
Ａ．Seroincidence: IgM(+) or 4-fold titer rising up or falling down
教授在講解這個段落的時候，有談到可用4倍抗體上升或下降來測血清發生率
财 上課有同學問到，為什麼要用4倍？
教授上課的時候有回答說：如果用2倍，有可能是dilution error..所以至少要4倍
關於這部分我還是不大了解，是不是能請教授再說明一下？謝謝！
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． 又有同學問到，為什麼抗體會下降？藉由complement fixation來看抗體的上ꐊ 升或下降，看哪段時間上升或下降。 這教授課堂上也有回答，不過我還是不
是很清楚，是不是能請教授再說明一下？謝謝！
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．教授上課的時候舉流行性感冒的例子，提到要用去年血清與今年血清作比較，要用
2個time point…但是要同時做？這部分我也不是很清楚，可以麻煩教授在說明一
下嗎?謝謝！
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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