THE MICROBIAL MENACE

JOHN SNOW — EPIDEMIOLOGY

The most terrible outbreak of cholera, which ever occurred in this kingdom, is probably that which took place in Broad Street, Golden Square, and the adjoining streets, a few weeks ago.
- John Snow, c. 1855

In 1854, as a new round of cholera swept through England, a surgeon named John Snow created a simple map with profound implications. He mapped the cases of cholera that appeared in a London neighborhood during a given week. The map helped him to identify their suspected point of origin, a centrally located water pump. Snow's map — in which he plotted new cases by location — is one of the earliest known epidemiological maps. It is also a milestone in epidemiology, the scientific study of epidemics with particular attention to their source, cause, and means of transmission.

Snow's systematic investigations also helped resolve a heated debate about how cholera was transmitted to people. By identifying contaminated water as a source of the disease, even before the specific contamination was visible, Snow was able to suggest a simple preventative measure: close the contaminated pump. The incidence of new cases, as Snow expected, immediately plummeted.

Vibrino cholera — a versatile bacterium. Cholera is caused by V. cholerae, a bacterium. Recent research suggests that V. cholerae has a "gene acquisition system" — called an integron — that allows it to acquire many different types of genes from other microbes and splice them into its own genome. This makes it easier for V. cholerea to acquire resistance and virulence factors from other bacteria.