Health Immunity and Disease - Modes of Disease Transmission

During an outbreak of a respiratory virus, it is found that the average infected person contacts $10$ people per day ($c = 10$), the probability of transmission per contact is $0.05$ ($\beta = 0.05$), and the person remains infectious for $4$ days ($d = 4$). Calculate the Basic Reproduction Number ($R_{0}$).

$R_{0} = 0.05 \times 10 \times 4$ $R_{0} = 0.5 \times 4$ $R_{0} = 2.0$

The $R_{0}$ value of $2.0$ means that every one infected person is expected to secondary infect $2$ other people in a completely susceptible population.

Distinguish between droplet transmission and airborne transmission based on particle size and behavior.

Droplet transmission involves particles $> 5 \mu m$ that fall to the ground quickly due to gravity. Airborne transmission involves nuclei $\le 5 \mu m$ that remain suspended in the air for long periods and can travel long distances on air currents.

This distinction is critical for determining whether a patient requires a standard surgical mask (droplet) or an $N95$ respirator (airborne).

A water source is contaminated with $Vibrio \ cholerae$. If the minimum infectious dose is $10^{6}$ cells and a person drinks $500 \text{ mL}$ of water containing $4 \times 10^{3} \text{ cells/mL}$, will they likely become ill?

$\text{Total cells} = \text{Concentration} \times \text{Volume}$ $\text{Total cells} = 4 \times 10^{3} \text{ cells/mL} \times 500 \text{ mL}$ $\text{Total cells} = 2,000 \times 10^{3} = 2 \times 10^{6}$

Since $2 \times 10^{6} > 10^{6}$, the person has ingested more than the minimum infectious dose and is likely to contract Cholera.