Today I want to share something I learned while reading some articles for a class. The article was regarding our measurement of disease in the population and how effects of strategies, interventions, and policies, are not always seen immediately.
Most of us are familiar with the latent period with regard to a disease, even if we do not know the terminology. Basically, the latent or latency period is the time from disease occurrence to the time of symptoms or clinical signs. So a person may become sick with a cold one day, but sneeze and cough the next, simply put.
The induction period is a little different and what I want to talk about now. There is very rarely if EVER only one thing or factor in the cause of disease. I have spoken about cancer as one of the illnesses that takes a long time to detect – for the cell changes to become a detectable tumor for instance, but I was only getting it half right. With cancer there are often initiators and promoters. With disease we may have three or four things that have to happen (most often unseen and unbeknownst to us) before the disease occurs. Some diseases will have symptoms the minute that last thing happens, and thus a brief or nonexistent latent period. The induction period however is staggered. If the factors, as explained in my reading, are the letters A, B, C, and D the time from A to D is As induction period and the time from B to D is Bs, etc. D has no induction period as once D occurs the person is diseased.
The induction period cannot be reduced exactly. If there are multiple factors that create a disease however and a subsequent factor can be stopped or postponed then the induction period is lengthened (a good thing) . The latency period, the time between induction and disease detection, might be shortened through screening and more sensitive tests.
Thus the recent study on which I lamented ( CT screening in smokers) does not change the time it takes for the cell mutations in the body to become cancer, but once initiated, the cancer might be discovered sooner by a more sensitive test.
This also speaks to the nature of genetics and environment. There is likely no disease that is 100% one or the other and most are multiple so whatever one can control – for instance physical activity, will keep the other, say genetic susceptibility, at a suspended induction mode.