Introduction: the infestation that doesn't start in your home
There's one situation pest control technicians recognise within three minutes of arriving on site, and that no standard treatment will fix: the flat is clean, well kept, has been treated twice, and yet it's reinfested every month. Cockroaches reappear behind the dishwasher, a persistent smell drifts up through the ventilation, bedbugs turn up despite no recent travel. That's when the technician asks the question that changes everything: "What about the neighbour, upstairs or next door?"
In a growing number of cases reported by the regional press — including a recent one documented by Ouest-France, where residents described an ordeal of cockroaches, bedbugs and foul smells coming from the home of a neighbour with Diogenes syndrome — the infestation never originated with the victim. It comes from a neighbouring flat that has become impossible to clean, to treat, sometimes even to open.
It's one of the most frustrating scenarios in pest control, because it brings together three worlds that communicate poorly: mental health, housing law and the technical side of pest treatment. This article explains how to recognise the situation, what you can realistically obtain, and in what order to act.
Diogenes syndrome: what we're really talking about
The term, popularised in 1975 by a paper in The Lancet, describes a clinical picture combining compulsive accumulation of objects or waste (hoarding), extreme neglect of domestic and personal hygiene (squalor), social isolation and, above all, a lack of awareness of the disorder (anosognosia). This is not laziness or malice: it is a behavioural syndrome often linked to psychiatric illness, early-stage dementia, bereavement or trauma.
Two practical consequences, essential to grasp before you act:
- The person will not ask for help. Slipping an indignant letter under the door has never achieved anything in this type of case. It can even lock the situation down further.
- Forced clear-outs without support fail. Social services and specialist charities record very high relapse rates when a property is cleared without medical and social follow-up afterwards.
For you, the neighbour, this means the solution will be neither quick nor something you can handle alone. It will run through a chain of actors: the building manager, the landlord, the municipal hygiene and health department (SCHS), the Regional Health Agency (ARS), and sometimes the local social action centre (CCAS).
Why the infestation travels through walls
A home in a state of squalor becomes what professionals call a reservoir. It concentrates the three resources pests are constantly seeking: accessible food, moisture, and an extraordinary density of hiding places (stacks of newspapers, cardboard, textiles, piled-up furniture).
German cockroaches: the champions of spread
Blattella germanica is the dominant species in multi-occupancy housing. A female produces an ootheca containing an average of 30 to 40 eggs, and can produce several over her lifetime. The full cycle takes roughly 6 to 8 weeks at 25–30 °C. In other words, one untreated reservoir flat can supply an entire building.
The routes of travel are always the same:
| Route | Why it works | Possible fix |
|---|---|---|
| Service ducts (water, electricity, telecoms) | Vertical, warm, never inspected | Seal with foam + fine mesh grille |
| Mechanical ventilation ducts | Continuous airflow, carries odours and insects | Insect grille with mesh ≤ 1 mm |
| Rubbish chutes and bin rooms | Permanent food source | Closure or intensified cleaning |
| Skirting boards and party walls | Micro-cracks at floor level | Acrylic filler, silicone sealant |
| Unused traps (siphons) | The water seal dries out | Pour water down them regularly |
Bedbugs: slower to spread, but more persistent
Cimex lectularius doesn't travel through ducts the way a cockroach does, but it migrates along skirting boards, cables and partition walls as soon as the population becomes dense or the host disappears. A cluttered home is a technical nightmare: heat treatment requires bringing everything up to temperature all the way through, which is impossible in the middle of tonnes of textiles and paper.
Rodents and flies
The build-up of organic waste attracts mice and rats, but also flies (Musca domestica, drain flies) and sometimes blowflies, whose appearance in numbers at a neighbour's home is a public health warning sign that should never be ignored: it can indicate a serious medical situation inside.
Step 1: document everything, before anything else
No procedure moves forward without evidence. And in this type of case, the burden of proof almost always falls on the complaining neighbour.
What to put together, from the very first week:
- A dated log: date, time, nature of the observation (number of cockroaches seen, smell, noises, flies). A notebook will do, but a daily record book holds its evidential value better than an editable file.
- Time-stamped photos of what you observe, inside your own home only — never photograph the interior of the neighbouring flat.
- Invoices for your own treatments: they show you are not the source of the problem and put a figure on your loss.
- An objective count. Sticky cockroach traps placed under the sink, behind the fridge and in the bathroom, checked every week, turn a subjective complaint into a numerical curve. It's the single most persuasive element when dealing with a building manager.
- Written statements from other occupants on your landing or in your riser.
A ten-page file with trap counts, dated photos and invoices achieves in a few weeks what a year of indignant emails never will.
Step 2: who to contact, and in the right order
If you are a tenant
Your point of contact is your landlord, not the neighbour. Article 6 of the French Act of 6 July 1989, as amended by the ELAN Act, requires the landlord to provide accommodation free from infestation by pest and parasitic species. Send a recorded delivery letter with acknowledgement of receipt setting out the facts, enclosing your file, and explicitly requesting intervention. That's what starts the clock running.
If you are a flat owner
Write to the building manager (syndic), who is responsible for maintaining the common parts — and the service ducts, ventilation system and bin rooms are part of them. Ask for:
- a building-wide or riser-wide pest treatment, not a flat-by-flat approach;
- the item to be added to the agenda of the next general meeting;
- a formal notice to the owner concerned under the building's co-ownership rules (the obligation not to cause nuisance to other occupants).
The public lever: SCHS, ARS, town hall
If the property poses a danger to the health or safety of its occupants and the neighbourhood, it falls under public health enforcement powers. Since the order of 16 September 2020, which came into force in 2021, these procedures have been consolidated under a single police power covering the safety and sanitary condition of buildings, exercised by the mayor or the prefect.
In practice:
- In a municipality with a Municipal Hygiene and Health Department (around 200 municipalities in France), it is the SCHS that carries out the inspection.
- Elsewhere, you refer the matter to the ARS via the departmental contact point, or to the single point of contact for substandard housing.
- The report can be filed online through the public service Histologe, rolled out nationwide to centralise reports of poor housing conditions.
The inspection may lead to an order to make the property safe or to remedy unsanitary conditions, with prescribed works, enforcement at the owner's expense if they fail to comply, and rehousing where appropriate.
The human side: CCAS and social services
In parallel, a report to the CCAS or to the town hall's social monitoring unit can trigger a home visit by a social worker. This is often the only route to a lasting solution: a clear-out followed by ongoing support, or even a legal protection measure (temporary guardianship, curatorship) if the person is no longer able to manage their home.
