Not exactly -- we're looking at two separate numbers here. This is where incidence vs. prevalence comes in.
Prevalence is the rate of cases of a disease in the population. Incidence is the rate at which NEW cases of a disease appear, per year. Depending on the disease, these interact in different ways.
Uganda's HIV prevalence was 30%, meaning that 30% of the population was infected. If there is, say, a 5% incidence of new infections per year, next year your prevalence will be 35%. (Forgive the sloppy math. You get the general idea.) If you can cut that incidence rate to 0, you have achieved a brilliant public health coup -- no new cases of HIV infection! -- but your prevalence next year is still 30%.
Contrast this for a second with something like the flu, which is both acute (short-term) and curable. Lots of people get the flu -- the incidence rate might be something like 90% for a given year, assuming no immunizations. However, it only lasts for a week and a half, so your prevalence -- the number of people who are off work and school with the flu at any given time -- is low. If you vaccinate and encourage good hygiene, you can cut both incidence and prevalence.
However, because HIV is a chronic, incurable disease, the only way for the number of infected people in the population to drop is for infected people to die (OK, and for uninfected people to be born, but leave that out for the moment). Other than that, you can't actually do anything about the prevalence. However, you CAN have an impact on the incidence, by reducing the spread of the disease -- with condoms (and even abstinence, heaven knows I'm not dissing it, but I think we need to be realistic here).
So in short, people dying of AIDS lowers the prevalence, but using condoms lowers the incidence.
Maybe I'm a little goofy but I don't see where you said anything that conflicts with what I said, you just made it sound less creepy. A rose by any other name would still be used to kill cockroaches after all.
it is not correct to say that the best way to prevent the spread of aids is to let the infected die. That will lower your prevalence, but won't do anything for your incidence (well, I suppose you could, if you were feeling draconian, kill 'em all off before they have a chance to infect anyone else, but that would be cruel and counterproductive in both economic and social terms). So you might as well do your best to keep them going for as long as possible, she said cheerily.
You're right on the condoms, though. And if you changed your sentence to read the best way to reduce the prevalence of aids is to let the infected die and use condoms, you'd be spot on.
...but of course, the letting-them-die bit would be bad for other reasons. See above.
It's sort of like heart disease. We try to encourage people to eat healthy, excercise and not smoke so they won't get it (i.e. lower the incidence). Once they get it, though, you need to try and help them live as long as possible. Prevalence tells you different things than incidence. High prevalence could mean:
- lots of people get this disease
or
- people with this disease die off fast but they pass it on to lots of other people beforehand
or
- not very many people per year get this disease, but they live with it a long time
Obviously the third option is the preferred way to go.
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timeasmymeasure
no subject
Date: 2005-03-02 07:15 pm (UTC)That the best way to prevent the spread of aids is to let the infected die and use condoms?
That's creepy, non?
no subject
Date: 2005-03-02 07:32 pm (UTC)Prevalence is the rate of cases of a disease in the population. Incidence is the rate at which NEW cases of a disease appear, per year. Depending on the disease, these interact in different ways.
Uganda's HIV prevalence was 30%, meaning that 30% of the population was infected. If there is, say, a 5% incidence of new infections per year, next year your prevalence will be 35%. (Forgive the sloppy math. You get the general idea.) If you can cut that incidence rate to 0, you have achieved a brilliant public health coup -- no new cases of HIV infection! -- but your prevalence next year is still 30%.
Contrast this for a second with something like the flu, which is both acute (short-term) and curable. Lots of people get the flu -- the incidence rate might be something like 90% for a given year, assuming no immunizations. However, it only lasts for a week and a half, so your prevalence -- the number of people who are off work and school with the flu at any given time -- is low. If you vaccinate and encourage good hygiene, you can cut both incidence and prevalence.
However, because HIV is a chronic, incurable disease, the only way for the number of infected people in the population to drop is for infected people to die (OK, and for uninfected people to be born, but leave that out for the moment). Other than that, you can't actually do anything about the prevalence. However, you CAN have an impact on the incidence, by reducing the spread of the disease -- with condoms (and even abstinence, heaven knows I'm not dissing it, but I think we need to be realistic here).
So in short, people dying of AIDS lowers the prevalence, but using condoms lowers the incidence.
/medical writer pontification
no subject
Date: 2005-03-02 09:03 pm (UTC)no subject
Date: 2005-03-02 09:34 pm (UTC)it is not correct to say that the best way to prevent the spread of aids is to let the infected die. That will lower your prevalence, but won't do anything for your incidence (well, I suppose you could, if you were feeling draconian, kill 'em all off before they have a chance to infect anyone else, but that would be cruel and counterproductive in both economic and social terms). So you might as well do your best to keep them going for as long as possible, she said cheerily.
You're right on the condoms, though. And if you changed your sentence to read the best way to reduce the prevalence of aids is to let the infected die and use condoms, you'd be spot on.
no subject
Date: 2005-03-02 09:40 pm (UTC)It's sort of like heart disease. We try to encourage people to eat healthy, excercise and not smoke so they won't get it (i.e. lower the incidence). Once they get it, though, you need to try and help them live as long as possible. Prevalence tells you different things than incidence. High prevalence could mean:
- lots of people get this disease
or
- people with this disease die off fast but they pass it on to lots of other people beforehand
or
- not very many people per year get this disease, but they live with it a long time
Obviously the third option is the preferred way to go.