To determine which organism in Table 15.2 most easily causes an infection, we need to look at the ID50 value for each organism. The ID50 value indicates the dose of a pathogen required to infect 50% of the subjects it is exposed to. A lower ID50 value corresponds to a higher infectivity, meaning that it requires fewer organisms to cause an infection in 50% of the subjects.
The ID50 values from the table are as follows:
- E. coli O157:H7: 20
- Legionella pneumophila: 1
- Shigella: 10
- Treponema pallidum: 57
We must compare these ID50 values to determine which organism has the lowest ID50, as this organism will be the most infectious.
Here are the ID50 values for quick reference:
- Legionella pneumophila: 1 (lowest ID50)
- Shigella: 10
- E. coli O157:H7: 20
- Treponema pallidum: 57
From this information, we conclude that Legionella pneumophila has the lowest ID50 value of 1. Hence, Legionella pneumophila is the organism that most easily causes an infection according to the figures in Table 15.2.
