An epidemic occurs when there is an abnormally high level of a disease at a particular time. It 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 spreads from one country to another and becomes prevalent around the world. New Zealand has experienced four pandemics, in 1890–94, 1918, 2009 and 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.
The severity of an epidemic is usually measured by its mortality rate (the number of people 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 can 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, which is 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 by the news media.
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. All these factors have changed considerably since the early 19th century, and vary from place to place.
Epidemiology is the branch of health science that studies the patterns of diseases, including epidemics. Since the 19th century research into diseases 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.
People are immunised against infectious diseases with vaccines, which contain either fragments of a disease germ or weakened germs. These prompt the body to produce cells and antibodies that protect the person from the disease. Vaccinations have been used since the 19th century. To prevent some diseases, such as measles, from circulating in the community, at least 95% of the population needs to be vaccinated. The Ministry of Health’s immunisation target is 95% of eight-month-olds fully immunised – in 2018, 91.7% were immunised.
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 natural disasters, these diseases can sometimes reappear and cause epidemics.
The historical pattern of epidemics in New Zealand reflects its isolation and relatively small population. The long sea voyage to New Zealand in the 19th century meant that most infectious diseases 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, simply disappeared after each local outbreak until they were reintroduced (usually from Australia), because the population was too small and thinly spread to sustain them. Some diseases did thrive 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 a third of all deaths. By 1900 the proportion was down to 15%, and in 2000 infectious diseases caused fewer than 7% of all deaths.
Evidence for epidemics in New Zealand is imprecise before 1872 because statistics on causes of death were not collected. Even after 1872 misdiagnosis and under-reporting were common. Doctors in the 19th century could not easily distinguish diseases with similar symptoms such as diphtheria, scarlet fever and measles. The cause of an infant death might be entered in official records as diarrhoea or ‘want of breast milk’, when typhoid was probably the real cause.
Māori deaths did not have to be registered with the government until the early 20th century, and even in the 1918 influenza pandemic hundreds of reported Māori deaths were not registered. Statistics for Māori births, deaths and marriages remained incomplete until the 1940s.
Rubella (German measles) was not a notifiable disease (one which had to be reported to public health services) 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 in or just before those years.
With the advent of bacteriology (the study of bacteria in relation to disease) in the late 19th century, identification of many diseases became more precise. New Zealand’s adoption of the Bertillon index of diseases (a list of known diseases) in 1909 reflects this. Since then, laboratory techniques for identifying diseases and their effects on the human body have been vastly improved, which makes modern statistics for epidemics more reliable.
The Ministry of Health monitors infectious diseases and manages programmes designed to contain and minimise their effects. In an international context, the ministry works closely with the World Health Organization (WHO), providing it with New Zealand health statistics and other information.
The Immunisation Advisory Centre based at the University of Auckland provides independent, factual information on immunisation and vaccine-preventable diseases.
The Institute of Environmental Science and Research (ESR) monitors infectious diseases and provides information to the Ministry of Health on disease rates and distribution, identifies outbreaks, monitors interventions and predicts emerging disease hazards.
European settlers brought new diseases to New Zealand in the early 19th century. Māori had little or no natural immunity to these diseases so suffered heavy mortality, particularly from measles and influenza.
Early influenza outbreaks among Māori were reported at Foveaux Strait in Southland between 1817 and 1820, and in the Bay of Islands and Mercury Bay in Coromandel in 1838 and 1839. In 1835 measles was reported among Māori working at the South Island whaling stations. According to T. A. Pybus: ‘The death rate was serious, and in many cases the people died as they stood. Even in later years skeletons [were] found far from their kaikas (settlements) … lying one across another indicating the suddenness of the end.’1
Early European settlements were often extremely unhealthy, lacking clean water supplies and effective sewage disposal. These created conditions favourable to the spread of infectious diseases. Typhoid and other bacterial infections were common, along with diphtheria, measles, whooping cough (pertussis), scarlet fever and tuberculosis. Infant mortality rates were high and medical treatments were often ineffective.
Respiratory infections caused many deaths, mostly attributed to bronchitis or pneumonia. Tuberculosis was a constant killer from this period – an endemic epidemic – until the 1950s.
Typhoid can usually be treated with antibiotics and rehydration. Untreated case-fatality rates vary between 10% and 30%, but can exceed 40%. Untreated typhoid typically follows four distinct stages, each lasting about a week. High fever, with delirium and agitation, is typical of the second week, along with diarrhoea resembling green-pea soup. In the third week dehydration and pneumonic complications may accompany the fever. Septicaemia, peritonitis and intestinal perforation are potentially fatal complications.
Typhoid was one of the most common diseases of 19th-century New Zealand. It is transmitted by water, milk or food contaminated by the faeces of an infected person. It is caused by the bacterium Salmonella enterica typhi, which produces symptoms of high fever, sweating, diarrhoea, headache and cough.
Typhoid was especially prevalent in fast-growing towns or on the goldfields, where cesspits often leaked into water supplies. Infants and young children were especially vulnerable. Registered typhoid deaths in New Zealand peaked at 323 in 1875.
Typhoid death rates declined in towns and cities as sanitation improved, but persisted in rural and Māori districts well into the 20th century.
In the 19th century Christchurch was one of the few places with a Board of Health and an active Medical Officer of Health. Dr Courtney Nedwill persuaded the city council to abolish cesspits and switch to a system of pans and ‘night-soil’ collection. This immediately reduced the death-rate from infectious diseases, even before the city completed an underground sewer system in 1882 (the first in New Zealand).
Dr Nedwill investigated a typhoid outbreak in Christchurch and at Sunnyside Asylum in 1881, tracing its source to a dairy farm in Lincoln Road. This led to an amendment to the Health Act that enabled the inspection of dairy farms by health officers. Despite this, milk-borne typhoid infections continued to cause epidemics in Auckland and other North Island towns until the 1940s.
The 1890s to the 1920s were dominated by two influenza pandemics (1890–94 and 1918), with annual epidemics in between.
Plague made its first and only New Zealand appearance in 1900, but it caused only a handful of deaths and disappeared after 1911. There were outbreaks of measles and whooping cough in 1907, and diphtheria in 1917.
Smallpox is a highly infectious viral disease, which used to be a major killer worldwide before the discovery of effective vaccination in the late 18th century. Mass immunisation campaigns in the 19th and 20th centuries eventually eradicated smallpox – it now exists only in laboratory storage.
Smallpox is at first hard to distinguish from chickenpox, but it is much more dangerous, and as the disease develops two types of case can be fatal: when the spots bleed and become septic, or if the rash extends into the air-passages, blocking the windpipe. Many survivors were forever marked by smallpox scars.
The most significant outbreak occurred in 1913 in Northland. It was traced to a Mormon missionary who caught smallpox on a ship sailing to New Zealand from Canada. After he attended a hui in Northland in April 1913 the disease spread rapidly. Most of the 2,000 reported cases were Māori, as were the 55 who died.
A mass vaccination programme was set up and travel restrictions imposed to slow the spread of infection. Newspapers made much of the outbreak, blaming the epidemic on lack of sanitation and poor living conditions among Māori, yet Māori were much more willing to receive vaccination than many Pākehā.
The epidemic was declared over by December 1913, though the last case was only notified in April 1914.
New Zealand’s worst disease disaster to date is the influenza pandemic of November 1918, which killed more than 50 million people worldwide, and 9,000 in New Zealand. No other recorded influenza pandemic has been so deadly – and nobody knows why it was so lethal.
It occurred in the wake of the First World War, when the movement of large numbers of troops by sea and rail greatly facilitated the spread of infection. Troops returning to New Zealand brought the virus from Europe. It reached epidemic proportions from late October, peaked in late November and was over by early December. Many people believed that the killer virus was brought to New Zealand by the passenger ship Niagara, which docked in Auckland on 12 October 1918 full of influenza sufferers. Prime Minister William Massey and Finance Minister Sir Joseph Ward were on board. Critics later argued that they arranged for the ship to avoid quarantine, but this was not the case, and the Niagara was later conclusively ruled out as the source of infection.
It has been suggested that the reason far more men than women died during the 1918 influenza pandemic is that men were typically the family breadwinners, so had to go out to work instead of staying home when sick to recover. Dairy farmers were at greater risk of collapsing or relapsing than other more sedentary professions, because they had to milk cows twice every day.
Symptoms exhibited by sufferers included chills, fever, runny nose, sore throat, coughs, headache and muscular pain. The real killer in 1918 was pneumonia – a secondary infection. The skin of some people who caught pneumonia darkened because of burst blood vessels. If the whole body became virtually black this often meant death was imminent. Later in life, sufferer Grace Stewart described her experience: ‘I was in bed for six weeks. My fingers and fingernails went black. My tongue was covered with some sort of fungus half an inch thick … The pain in the whole of my body was terrible.’1
Unlike in other countries, where male and female deaths were about equal, New Zealand death rates for males were double those for females in the worst-affected age groups. The Māori death rate was more than eight times that for Pākehā. The highest regional death rates for Pākehā were in Southland, King Country, Wellington and Auckland. Auckland city had the largest Pākehā death toll at 1,128 (7.6 per 1,000). Nationwide, 135 Pākehā children lost both parents, while 6,415 lost one.
Improved sanitation and water supplies virtually eliminated the major bacterial diseases of the 19th century from New Zealand’s European population by the 1920s. Epidemic diseases were no longer major causes of death. Non-communicable diseases such as cancer and heart disease replaced them as the leading causes of death.
Polio is probably a very old disease – a 3,500-year-old Egyptian wall carving shows a man with the characteristic withered leg of a polio victim.
Apart from isolated outbreaks of diphtheria and typhoid, and continued high death rates from tuberculosis, the most alarming infectious disease of this era was poliomyelitis (polio), an acute viral disease affecting the spinal cord and nervous system. Symptoms include fever, headache, malaise, pain and stiffness in back and neck, and partial or complete paralysis of limbs or the entire body. Case-fatality rates from paralytic polio have varied from 2% to 10%. New Zealand experienced polio epidemics in 1916, 1925, 1927, 1937, 1948–49, 1952–53 and 1955–56.
Polio is typically a disease of children and adolescents, but the risk of paralysis increases markedly with the age of the patient, making young adults especially at risk if they catch this disease. In early outbreaks there was no effective treatment so careful nursing and palliative care (which alleviates symptoms rather than the cause) were the main medical responses. The lives of seriously paralysed patients could only be saved by long periods in a compression chamber or ‘iron lung’. Survivors with a withered leg were fitted with strengthening callipers, which helped them walk. Public health campaigns in the 1950s stressed personal hygiene – schools provided buckets of disinfectant in their toilet blocks.
Effective polio vaccines were developed in the 1950s. Jonas Salk’s inactivated vaccine of 1955 was followed by Albert Sabin’s weakened live virus oral vaccine in 1960. In New Zealand use of the Salk vaccine delayed the reappearance of polio between 1956 and 1961. After this a mass immunisation campaign using the Sabin oral vaccine achieved high population coverage and eliminated the polio virus from New Zealand.
Since the 1970s immunisation programmes have successfully controlled some diseases, such as hib disease (haemophilus influenzae type B, which can cause meningitis and epiglottitis), which has been virtually eradicated. A campylobacteriosis (a gastro-intestinal disease mainly caused by eating chicken that has not been properly cooked) epidemic peaked in 2006 and then abated, probably due to new regulatory standards in the poultry industry.
Though epidemics have become less frequent, studies have found that hospital admission and discharge rates for infectious diseases have increased since at least the 1980s. This counters the prevailing wisdom that these diseases have become less of a burden. Because of air travel, New Zealand is no longer an isolated country and has become affected by more diseases as they spread through the world; notably HIV/AIDS, SARS (seasonal acute respiratory syndrome) and influenza. The 2009 influenza A (H1N1 – generally known as swine flu) pandemic caused more than 3,000 cases and 20 deaths in New Zealand. Despite improved uptake of annual influenza vaccination, seasonal influenza epidemics continue to have an impact, especially on older people. On average, about 40 deaths are linked to influenza each year. The 2020 COVID-19 coronavirus pandemic was characterised by influenza-like symptoms and also affected older people disproportionately.
Meningococcal disease is a bacterial disease. It causes meningitis (an inflammation of the protective membranes covering the brain and spinal cord) and septicaemia (blood poisoning). Severe infections can cause shock, coma and death within a few hours if not treated quickly with antibiotics. Meningococcal disease can have serious long-term effects for survivors, including deafness and epilepsy.
An outbreak of meningococcal group A in Auckland in 1985–86 was controlled by mass immunisation. Meningococcal disease reached epidemic proportions in the 1990s and early 2000s.
A new group B epidemic started in 1991 – 78 cases were recorded then, compared to an average of 51 per year (1.5 cases per 100,000 people) prior to this – and quickly became a major outbreak.
The highest infection rates were among Māori and Pacific Island children under five years of age. The upper North Island was the most affected, particularly Northland, Auckland and Rotorua. The epidemic peaked in 2001 with 650 cases (17.4 cases per 100,000 people), and 252 deaths were attributed to meningococcal disease between 1991 and 2007.
In 2005 scientist Jeanette Adu-Bobie fell ill with meningococcal septicaemia caused by meningococcal B after working in an Environmental Science and Research (ESR) laboratory in Porirua. She had both legs, her left arm and the fingers on her right hand amputated to save her life. Initially, ESR said they could find no link between her workplace and her illness. However, later reports concluded that it was highly likely that this is where Dr Adu-Bobie caught the disease. She received compensation of $117,000.
A new vaccine developed specifically for the New Zealand strain of meningococcal group B was introduced in 2004. More than 1.1 million children and young adults were immunised. This was one of New Zealand’s largest mass-immunisation campaigns and involved schools, primary health care providers and district health boards. It cost over $200 million. Reported cases declined from 342 in 2004 to 105 (1.7 per 100,000) in 2007, by which time the epidemic was regarded as controlled.
In the 21st century the Ministry of Health developed new vaccination programmes to protect future generations from highly prevalent viruses that were associated with particular health risks. In 2008 it introduced a programme that made vaccination against the HPV (Human Papillomavirus) available to young women born in 1990 and 1991. This was directed at protecting girls from the sexually transmitted HPV virus before they became sexually active. HPV has been linked to carcinoma of the cervix and invasive cancer. In 2017 this vaccine became free to everyone aged 9–26. Those under 15 receive two doses of the vaccine, six months apart. HPV virus has also been linked to increased risk of cancers of the mouth and tongue.
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