Of the Age Concern organisations, 92 per cent had been involved with clients in severe domestic squalor in the last year.
Around 93 per cent of territorial and domestic councils had dealt with people in this position.
Public health physician Dr Jonathan Jarman said severe domestic squalor referred to homes which were cluttered in rubbish and infested by vermin.
In the most extreme cases, excrement and decomposing food were strewn on the floors and the stench was “unbearable to all but the occupant.
“The conditions are so bad that most people would say that the house was not fit for human occupation,” said Jarman.
“Common features for people living in these conditions include lack of concern, social withdrawal, hostile attitudes, being older, and in many cases a stubborn refusal of help.”
Jarman said there were significant health risks for these people as well as their family, carers, visitors, neighbours and pets. Rundown houses also posed a fire risk.
“Because of the social isolation and distrust of others, people who live in squalor can suffer a lonely death and remain undiscovered for a long period of time,” he said.
An Australian survey found around 0.1 per cent people aged 65 years and older lived in severe squalor.
There was limited data in New Zealand, and the survey aimed to get a preliminary estimate. Among Age Concern clients, around 4 per 100,000 people lived in houses unfit for human occupation. This was likely to rise as the population aged, the briefing noted.
The survey also asked respondents about the best solutions for people living in unclean, messy and unhygienic properties.
The top-ranked interventions were having a lead agency which coordinated a multi-agency response, and having a budget for cleaning homes.
The briefing said legal solutions could be costly and prolonged. Councils were often left with large bills because people living in squalor typically had little money for clean-ups.
It cited British research which indicated that longer-term, less formal approaches by social and mental health services were likely to be the most useful approach.