[bonesmccoy]

Your comments appreciated.

In answer to my posited question on rate of spread of disease, I'd like to submit this analysis.

Assuming the following:
There is a rate of potential contagion defined by the number of people the index case meets in a set amount of time.

Pc = people contacted per unit time
Pnc = people never contacting agent

Each agent has a rate of "successful" infection, where a given susceptible person is exposed to the germ and becomes symptomatic.

Ki = ratio of people infected over total people contacted per unit time.

Ki = Pi/Pc, where Pi = number of infected people

Let's assume the following:
A. a city of 20,000 people, where each person regularly interacts with 20 people per day.

B. 50% of the contacts per day are uncontacted and 50% are regularly contacted individuals.

C. The organism successfully infects 50% of the contacts and creates immunity in the remaining 50%.

D. Of those infected, 30% become symptomatic.

E. Illness has one week incubation period.


Here are the numbers:

Week One:
1 index case exposes 20 people per day (140 per week).
If 50% of all exposed people get infected, 140 contacts creates 70 infected individuals.

Week Two:
1 index case gets ill and is isolated at home/hospital (no longer spreading disease)
70 infected cases contact 20 people per day (infecting 4900 people over the week).

Week Three:
If 30% of infected cases become very ill, 21 cases (who became ill in week one) will fall critically ill (and thus, be removed from spreading disease). This means that roughly 4950 people are still spreading disease.

Week Four:
As the disease is identified in week three, the 21 index cases will alert national health authorities regarding the spread of disease. However, the undiagnosed infected people will still be spreading disease (and that's 4950 people). If they are continuing in their regular activities (and reach 140 new individuals per week), they will infect 346430 people by weeks end.

If the 30% of the people who got infected in week two become ill in Week Three, over 1400 patients will need admission to the hospital in that area.

It is unlikely that hospital capacity can handle that number of cases.

This would necessitate a national emergency with mobilization of national guard capability. Since national guard capabilities may be stretched thin if foreign threats require deployment, civilian capacity will need to handle one thousand cases in one week without national guard intervention.

Perhaps this is the starting point of analysis for civilian medical response capabilities.