Household crowding an avoidable health risk

This Issue This is a part of the Preventing disease feature

By - , Build 98

Although household crowding is relatively uncommon in New Zealand, levels are high enough to contribute to serious health problems, particularly for vulnerable groups.

Figure 1: Hospitalisation rates in HNZC applicants and tenants according to household crowding level. These are average annual rates for the February 2003 to June 2005 period found in the Housing, Crowding and Health Cohort Study.
Figure 1: Hospitalisation rates in HNZC applicants and tenants according to household crowding level. These are average annual rates for the February 2003 to June 2005 period found in the Housing, Crowding and Health Cohort Study.
Healthy Housing open 2
Prime Minister Helen Clark and the meningococcal disease risk factors research team in Onehunga in 2001 opening the first house upgraded as part of HNZC’s Healthy Housing programme.

When discussing household crowding, it is useful to consider the concepts of occupancy level, density level and crowding level.

Occupancy level is the number of people per dwelling. This measure does not include the dwelling size so cannot indicate whether a dwelling is crowded. However, since most housing has a fairly modest number of rooms (median of three bedrooms in New Zealand) high occupancy usually means a dwelling is crowded.

Density level is the number of people for a particular amount of space, for example people per room or bedroom, or people per square metre or square metres per person. These measures give an indication of crowding level.

Crowding level measures relate density level to an established standard or threshold so they can indicate whether a particular dwelling is crowded.

Prime Minister Helen Clark and the meningococcal disease risk factors research t
Prime Minister Helen Clark and the meningococcal disease risk factors research team in Onehunga in 2001 opening the first house upgraded as part of HNZC’s Healthy Housing programme.

Choice of crowding measures

Two well-established measures are the American Crowding Index (ACI) and Canadian National Occupancy Standard (CNOS).

The ACI is derived by dividing the number of usual household residents by the number of rooms (excluding bathrooms, porches, balconies, foyers, halls or half-rooms). A house is considered crowded if there is more than one person per room.

The CNOS sets the bedroom requirements of a household according to the composition criteria of:

  • there should be no more than two people per bedroom
  • parents or couples share a bedroom
  • children under 5 years may share a bedroom
  • children under 18 years of the same sex may reasonably share a bedroom
  • a child aged 5 to 17 years should not share a bedroom with one under 5 years of the opposite sex
  • single adults 18 years and over and any unpaired children require a separate bedroom.

A house is deemed to be crowded if any of these conditions are not met. This measure is reported as bedroom deficit. The CNOS has been adopted as the preferred measure of crowding by Statistics New Zealand, Housing New Zealand Corporation (HNZC) and the Ministry of Social Development.

Increased crowding for some

Statistics New Zealand has used census data to analyse the distribution of household crowding. They published a detailed analysis using the 2001 Census (available on www.stats.govt.nz/analytical-reports/housing/ under Housing statistics-crowding analytical report).

Figure 1: Hospitalisation rates in HNZC applicants and tenants according to hous
Figure 1: Hospitalisation rates in HNZC applicants and tenants according to household crowding level. These are average annual rates for the February 2003 to June 2005 period found in the Housing, Crowding and Health Cohort Study.

Household crowding, measured by a deficit of one or more bedrooms, was relatively uncommon in New Zealand in 2001, accounting for 5.1% (65,091) of households. Only 1.2% (15,453) required two or more bedrooms. Although crowding levels have generally fallen in New Zealand over the last few decades, this has not been the case for all groups.

There was a clear increase in crowding levels for those living in rental housing in Auckland during the 1990s. Crowding is highly concentrated in low-income families with children, households containing Maori and Pacific people and households with recent migrants.

Infectious disease link

There is good evidence that household crowding is a risk factor for several important infectious diseases. It may also predispose inhabitants to some injuries (particularly burns), chronic diseases (such as heart disease), and social problems (such as educational difficulties), though the evidence for these associations is less robust.

The importance of household crowding for infectious disease transmission is logical for diseases where humans are the reservoirs for infection. Household crowding increases the number of contacts that household members have over a period of time and therefore increases the ‘reproduction number’ for infection within that population. This effect is likely to be particularly important for children, who spend most of their time in the home environment.

Household crowding has been linked to the following infectious diseases:

  • Bacterial meningitis and septicaemia in children – a strong association has been found for meningococcal disease and Hib (Haemophilus influenza type b) disease.
  • Bronchiolitis in children – infections caused by respiratory syncytial virus in infants frequently result in hospitalisation.
  • Enteric infections in children – some infections acquired via the mouth, notably Helicobacter pylori infection and hepatitis A.
  • Tuberculosis (TB) – has long been associated with crowded living conditions, though this risk is still not well researched.
  • Pandemic influenza – 50% of influenza transmission occurs in the home so household crowding is expected to increase the risk of pandemic influenza transmission, though this has not been quantified.

There is suggestive evidence for other infectious diseases, like rheumatic fever, skin infections and cellulitis, being linked to household crowding, but more research is needed.

Health and social housing study

As with most potentially harmful exposures, the problem of household crowding becomes important if the exposure occurs for a long period, and involves particularly vulnerable household members. This is often the situation when low-income families live in rental accommodation for many years and are sometimes forced to double-up with other families.

He Kainga Oranga / Housing and Health Research Programme at the University of Otago (Wellington) has set up a cohort study to investigate health outcomes among those living in social housing. The Housing, Crowding and Health Cohort Study is analysing hospitalisations that occur in the approximately 225,000 HNZC tenants and applicants (see Figure 1). This study shows that crowding, as measured by a deficit of one or more bedrooms, is very common in applicant households (49%) and decreases for tenants (29%). A particularly exposed group are housing applicants living with other families where 80% of these ‘double-up’ households were classified as crowded using the CNOS.

This cohort study has found that overall hospitalisation rates are higher among those living in crowded households, particularly those that are short of two or more bedrooms (see chart from Characteristics of cohort members and their hospitalisations, available from www.wnmeds.ac.nz/academic/dph/research/housing/crowding.html).

Affordable, suitable housing needed

Reducing levels of household crowding is a challenge. This is partly because crowding levels are determined by both the dwelling and the people dwelling in it. It is technically impossible to design and build a house that cannot become crowded by having too many people living in it. Strategies for reducing household crowding include:

  • provision of an adequate supply of affordable, suitable housing
  • specific programmes to reduce crowding levels for high-risk populations
  • improved regulation of crowded houses.

When housing is in short supply and expensive, then low-income families will frequently respond by doubling-up. Similarly, if the available housing stock is poorly matched to the housing needs of some population groups, then household crowding may occur. An example is the shortage of housing with more than three to four bedrooms to meet the housing needs of larger Pacific Island families. The Housing and Health Research Programme is working with the Victoria University of Wellington School of Architecture and HNZC to design a prototype extended family house for 11 people, which will be built in Porirua East.

The best New Zealand example of a programme to reduce crowding levels in high-risk populations is the Housing New Zealand Healthy Housing Programme. It aims to decrease health risks and improve access to health and welfare services for those living in HNZC properties. This programme is important as it has the potential to reach all HNZC tenants, about 5% of the New Zealand population. Initial evaluation suggests that it has been successful at reducing levels of household crowding, and has reduced hospitalisation rates for some diseases.

The potential to enforce lower levels of household crowding is probably quite limited. The Department of Building and Housing’s review of the Building Code, published in May 2006, notes, ‘The Building Code cannot prevent overcrowding that causes health problems, because it cannot dictate the number of people that occupy a space.’ There are provisions in the Health Act 1956 to regulate nuisances caused by the condition and use of dwellings. The Housing Improvement Regulations 1947 made under this Act do specify controls on overcrowding but these are rarely used.

Overcrowding avoidable

Household crowding levels in New Zealand remain high enough to contribute to serious health problems, particularly infectious respiratory diseases. Reducing this avoidable problem ultimately depends on an adequate supply of affordable, suitable housing.

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Figure 1: Hospitalisation rates in HNZC applicants and tenants according to household crowding level. These are average annual rates for the February 2003 to June 2005 period found in the Housing, Crowding and Health Cohort Study.
Figure 1: Hospitalisation rates in HNZC applicants and tenants according to household crowding level. These are average annual rates for the February 2003 to June 2005 period found in the Housing, Crowding and Health Cohort Study.
Prime Minister Helen Clark and the meningococcal disease risk factors research t
Prime Minister Helen Clark and the meningococcal disease risk factors research team in Onehunga in 2001 opening the first house upgraded as part of HNZC’s Healthy Housing programme.

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