Kōrero: Epidemics

Whārangi 1. Epidemics, pandemics and disease control

Ngā whakaahua me ngā rauemi katoa o tēnei kōrero

An epidemic occurs when there is an abnormally high level of a disease in a country at a particular time. The term usually refers to infectious diseases, but it is also possible to have epidemics of non-infectious diseases such as heart disease and diabetes, and conditions such as obesity.

A pandemic occurs when an epidemic becomes prevalent around the world. New Zealand has experienced four pandemics, in 1890–94, 1918, 2009 and since 2020.

An endemic disease is continually present in a population at a low rate, or with a low death rate. An example of this in New Zealand in the 21st century is hepatitis B.

Measuring epidemics

The severity of an epidemic is usually measured by its mortality rate (the proportion of the population who die from the disease). Epidemics of some diseases will have a high morbidity rate – make a lot of people ill – but not cause many deaths. They will cause considerable social and economic disruption if large numbers of people have to stay at home.

Another measure of the severity of an epidemic is the case–fatality proportion, the percentage of people with the disease who die from it. An epidemic may affect a very small proportion of the population yet prove dangerous to those who catch the disease. Most pass unnoticed by the general public, unless increased hospital admissions or an alarming number of deaths are reported.

Red years

Rubella (German measles) was not a notifiable disease (one which had to be reported to public health authorities) and caused very few deaths, but it did cause foetal abnormalities, including deafness. Unusually large numbers of deaf children were born in New Zealand in 1899, 1939 and 1941–42, which suggests that rubella was prevalent during or just before those years.

The severity of an epidemic depends on factors such as the size and health of the population, the nature of the infectious organism, the speed and ease of travel, and the availability of medical services and effective treatments. These factors vary from place to place, and have changed considerably since the early 19th century.

Epidemiology and disease control

Epidemiology is the branch of health science that studies the patterns of diseases, including epidemics. Research into diseases since the 19th century has led to some that were feared killers in the past – for example, influenza and smallpox – being controlled or eliminated by immunisation with a vaccine. However, New Zealand’s immunisation rates are lower than those of many other developed countries.

Some diseases that caused high mortality in the 19th century, such as cholera, scarlet fever and typhoid, have virtually disappeared from developed countries (including New Zealand) due to improvements in personal hygiene, public sanitation, nutrition and health services. However, when developed infrastructures collapse during wars or following natural disasters, these diseases can sometimes reappear and cause epidemics.

Historical epidemic patterns

The historical pattern of epidemics in New Zealand reflects the country’s isolation and relatively small population. The long sea voyage to New Zealand in the 19th century meant that most infectious diseases carried on board had died out by the time the ship arrived.

Some migrant ships suffered high infant mortality from scarlet fever and gastrointestinal infections. Quarantine regulations from the 1870s were aimed at preventing the arrival of unwelcome infections, especially smallpox. In 1872 a smallpox outbreak in Auckland was traced to the SS Nebraska.

Until the 1920s some diseases, such as measles and rubella, disappeared after each local outbreak until they were reintroduced (usually from Australia), because the population was too small and thinly spread to sustain them. Other diseases thrived in New Zealand’s small urban centres. In 1875, typhoid was widespread in towns and cities – there were 323 deaths.

Deaths from infectious diseases have generally declined since records began in the late 19th century. In the 1870s, infectious diseases accounted for one-third of all deaths. By 1900 the proportion was down to 15%, and in 2000 infectious diseases caused less than 7% of all deaths.

Me pēnei te tohu i te whārangi:

Geoff Rice, 'Epidemics - Epidemics, pandemics and disease control', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/epidemics/page-1 (accessed 24 May 2024)

He kōrero nā Geoff Rice, i tāngia i te 5 May 2011, reviewed & revised 8 Feb 2024