THE DEBATABLE JOYS OF PROGRESS!

We all know much more about epidemic diseases than we did a couple of years ago. We know that a disease-causing organism is called a pathogen. We are also more familiar than we were with the ways a pathogen can jump from one victim to another. The agent of transfer — fleas in the Black Death, used needles in HIV/AIDS, mosquitos in malaria — is called the vector.

Drinking water has, over the centuries, been an excellent vector. In the early days of European settlement in New Zealand, if you weren’t drowned crossing a river in flood — known as ‘the New Zealand way of death’ — you would probably die from typhoid in the embryonic towns, due to the very common contamination of water supplies by sewage.

In 1993 more than 100 citizens of Milwaukee, Wisconsin — previously most famous for its beer — died in an epidemic of water-borne disease.

The solution to the contaminated water problem is either to stop the pathogen getting into the water or to kill it if it does, by adding chlorine to the water or boiling the water. Both methods have problems. Boiling is time-consuming and can be dangerous; it has been suggested in Britain that the danger to the elderly and infirm from the boiling water is greater than the danger posed by water-borne pathogens. Chlorine has an unpleasant smell, especially at higher concentrations, and, it turns out, can cause pitting in copper hot water cylinders (HWCs) under certain conditions, leading to unfixable leaks in the cylinders.

A gastroenteritis outbreak in Hawke’s Bay

In August 2016 a serious outbreak of gastroenteritis occurred in Havelock North. It affected more than 5000 people — about a third of the town’s inhabitants — with 45 hospitalised. Those are the indisputable facts. It is probable that four people died as a result, and that the pathogen was the bacteria campylobacter, from sheep. The accepted theory is that floodwater carried sheep faeces to a below-ground pump-head that wasn’t sufficiently sealed to