A 60-Bed Community Hospital Found 5 Patients Who Caught Dengue While Admitted, From Mosquitoes in the Treatment Tank Behind the Ward
Last updated: 7 Sep 2026 | 7 Views |
A true story from a 60-bed community hospital in northern Thailand
A 60-Bed Community Hospital Found 5 Patients Who Caught Dengue While Admitted, From Mosquitoes in the Treatment Tank Behind the Ward
When a patient admitted for one illness acquires another inside the hospital, and the lesson every healthcare facility should read
A 60-bed community hospital in northern Thailand identified five patients who acquired dengue while admitted, in a single rainy season. The outbreak investigation traced it to the sewage treatment tank and the landscaping behind the inpatient building. Here is what the infection control team found, and how the AIROFOG AT35 thermal fogger became part of the prevention system.
Dr Worapon, 43, directs a 60-bed community hospital in a northern province, serving a catchment of about 32,000 people. He says the thing that has cost him the most sleep in his career is not a difficult case. It is a patient who became more ill because they came to his hospital.
Last rainy season the inpatient nursing staff reported patients admitted for other conditions developing high fever during their stay. Testing confirmed dengue, and when onset dates were compared against admission dates, the intervals were consistent with hospital-acquired infection in five patients.
Two of them were elderly patients with comorbidities whose condition deteriorated badly enough to require transfer to the provincial hospital. Dr Worapon says he had to explain this to their families, and that was the hardest conversation of his professional life.
What the investigation team found behind the inpatient building
The hospital's infection control team, with officers from the district health office, surveyed the entire site at six in the evening — an hour nobody had ever surveyed before, because routine sanitary inspections happen during office hours.
The first finding was the sewage treatment tank behind the inpatient building: two damaged covers and ventilation openings with no insect mesh. At six in the evening the team could see clouds of mosquitoes around it, and the tank sits roughly 15 metres from the inpatient ward windows.
The second was the landscaping around the building — dense shrub planting installed for shade under a green hospital initiative, which had become the best mosquito harbourage on the site, along with dozens of plant saucers holding water.
The third, which shocked the team most, was inside: flower vases brought by visiting relatives and left in the wards, with water rarely changed; water containers in some patient bathrooms; and uncovered reserve water drums kept for supply interruptions.
Why hospitals warrant particular vigilance
Dr Worapon explains that hospitals stack risk factors on top of one another. First, infected and uninfected people occupy the same space. A dengue patient admitted for treatment is a reservoir, and the patient in the next bed admitted for something else is the person at risk.
Second, vulnerable groups are concentrated. Most inpatients at a community hospital are elderly people, patients with comorbidities and small children — precisely the groups in whom dengue is significantly more severe.
Third, patients cannot move away. Someone bed-bound or sedated cannot brush a mosquito away or change position like a healthy person, so they are bitten many times more in the same period.
Last is the building. Many community hospitals use natural ventilation to save energy, with windows and louvres permanently open and insect screening that has degraded with the building's age — so mosquitoes reach the wards easily.
The costs the hospital and the health system absorb
Five hospital-acquired infections added roughly 34 patient-days. In a community hospital with limited beds, that means beds that should have treated other patients were consumed by an entirely preventable problem.
The two patients who deteriorated required transfer to the provincial hospital, which carries transfer costs, substantially higher treatment costs, and the burden on families of travelling far from home to sit with them.
Systemically, a report of hospital-acquired infection affects quality indicators and must be reported through the system, triggering review and remediation that consume both time and budget.
But the true cost, Dr Worapon says, is trust. Once local people start saying that you go in to be treated and come home with something else, the trust a community hospital built over decades is shaken immediately — and it spreads to every other service, from antenatal care to immunisation.
The system the hospital built afterwards
Dr Worapon convened a working group across infection control, sanitation and maintenance, and set the measures out in three layers, the same way the hospital already handles other infection control.
The first layer is source elimination: repairing the treatment tank covers and fitting insect mesh to every ventilation opening, replacing planters so no saucers are needed, requiring ward flower vase water to be changed daily, and fitting lids to every reserve water drum.
The second layer is exclusion: surveying and repairing every insect screen in the wards, fitting air curtains at the main doors, and where possible placing dengue patients in rooms with intact screening, separated from the general wards.
The third layer is thermal fogging around the buildings to control adult mosquitoes, concentrating on the treatment tank, the landscaping around the inpatient building, the boundary, and the kitchen and waste storage areas. The hospital chose two AIROFOG AT35 units, assigned two maintenance staff as responsible operators, and fogs twice a week through the rainy season.
What it actually costs
Patients acquiring an additional illness during admission
Hospital-acquired infection is the highest priority for any health system, because the patient came in for one condition and left with another — particularly serious when they are elderly with comorbidities and therefore at far greater risk of severe dengue.
Beds and resources consumed by a preventable problem
Thirty-four additional patient-days in a hospital with only 60 beds means beds that should have treated other patients were used on a problem preventable through environmental management.
Community trust built over decades
A community hospital runs on local trust. Once people start saying you go in and come home with something else, that trust is immediately shaken, and it affects every other service the hospital provides.
The health of the clinical staff themselves
Nurses and staff working night shifts in a ward with mosquitoes carry the same risk as the patients — and in a community hospital with limited staffing, one nurse falling ill disrupts the entire ward roster.
Why the usual fixes do not work
Relying on insect screening alone
Necessary and worth doing, but insufficient, because screening in older buildings degrades and develops gaps you cannot see. Doors open constantly for bed transfers and visitors, and screening does nothing to reduce the mosquito population outside.
Using aerosol cans inside the wards
Inappropriate in a space with respiratory patients, elderly people and children. It also covers a tiny area, dissipates quickly, and needlessly worries patients' families.
Installing electric insect traps in the wards
They work within a very limited radius, and the noise and light interfere with patients' rest. Above all they do nothing about the source, which is the treatment tank and the landscaping outside.
Waiting for the municipality to spray
Local authorities have limited resources across a whole sub-district. A hospital, which concentrates the most vulnerable people anywhere in the area, should not be in a queue and needs the capability to act at the frequency actually required.
Conducting sanitary inspections only during office hours
This is why the problem went unnoticed for years. Aedes feeds heavily at dawn and dusk. An inspection at ten in the morning simply will not show what six in the evening shows.
Hospitals should manage mosquitoes exactly as they manage other infection risk — systematically and measurably
Dr Worapon's central point is that hospitals already have excellent infection control systems for contact and airborne transmission, but have never had the same system for vector-borne disease, even though the principles are identical.
Those principles are: eliminate the source, prevent access to the patient, and continuously reduce the pathogen or vector load in the environment. For mosquitoes that means removing breeding sites, repairing screening, and consistently fogging to control adults around the buildings.
A thermal fogger is the right tool for that third element, because the fog drifts into the shrubbery around the buildings, the treatment tank ventilation openings, beneath raised structures and along the boundary — harbourage nothing else reaches. Fogging outdoors means patients inside are unaffected.
And the machine must belong to the hospital, because the required frequency is twice a week through the rainy season plus an immediate application whenever a dengue patient is admitted — a rhythm no contractor can supply. Hence the AIROFOG AT35, with its stainless body and domestic service network.
10 reasons the AIROFOG AT35 thermal fogger solves it
1. Fog reaches the treatment tank, shrubbery and spaces beneath buildings
The source of mosquitoes at a hospital is the sewage treatment tank, the landscaping around the wards, the space beneath raised structures and the boundary. The AIROFOG AT35 produces a fog that genuinely drifts into all of these — something screening and insect traps cannot do at all.
2. Applied outdoors, so patients inside are unaffected
The key point for a healthcare facility is treating the source without disturbing patients. Concentrating the application outside the buildings substantially reduces the mosquitoes reaching the wards, with no need to fog inside spaces holding respiratory patients and elderly people.
3. A 100 percent stainless steel body that handles work near the treatment tank
The area around a sewage treatment tank combines high humidity with corrosive gases. A less resistant body corrodes within a few years. Full stainless construction gives hospital equipment a long service life — important when spending public budget you must account for.
4. Compliant with Thailand's government standard equipment specifications
For community hospitals, sub-district health promoting hospitals and public healthcare facilities, conformity with the standard equipment schedule means the budget request and reference price sit correctly within the category and acceptance requires no reinterpretation.
5. Maintenance staff can operate it themselves
Community hospitals have limited staffing and no specialist pest team. The AT35 is simple enough to train two or three maintenance staff as responsible operators, so fogging becomes a scheduled routine rather than something that waits on anyone else.
6. Immediate application whenever a dengue patient is admitted
This is the single most valuable capability for a healthcare facility. When a dengue patient is admitted, the hospital should fog around the buildings the same day, to reduce the chance of mosquitoes acquiring the virus from that patient and biting others. Ownership makes same-day action possible.
7. Runs both water-based and oil-based formulations
Healthcare facilities must choose chemistry carefully and use properly registered products. Accepting both formulation types lets the hospital follow Department of Disease Control guidance and rotate products through the year to slow resistance.
8. Certified to German and British standards
For facilities undergoing quality accreditation and needing documentary references within their infection control system, internationally certified equipment is evidence that can be presented and is recognised by assessors.
9. 100 percent quality control before dispatch
Every unit is run-tested before shipping, which matters greatly for government acceptance inspection and assures the hospital that the machine works from day one rather than entering a warranty process.
10. A Thai service centre with genuine parts and 10-plus years of technician experience
A hospital never stops, and the rainy season means months of continuous use. Domestic service and genuine parts mean no month-long wait on overseas shipments — for a healthcare facility, non-negotiable.
Before the thermal fogger
- 5 patients acquiring dengue during admission
- 2 elderly patients deteriorating and requiring transfer to the provincial hospital
- Roughly 34 additional patient-days
- Damaged treatment tank covers and ventilation openings without insect mesh
- Degraded ward insect screening that nobody had surveyed
- Sanitary inspections only during office hours, so the problem was never visible
After the thermal fogger
- No hospital-acquired dengue cases the following rainy season
- Treatment tank covers repaired and insect mesh fitted throughout
- Every ward insect screen surveyed and repaired
- Twice-weekly fogging through the rainy season by the hospital's own staff
- Immediate fogging every time a dengue patient is admitted
- Fogging records entered into the hospital's infection control system
The three-step process
1. Survey the site at six in the evening
Assemble a joint team from infection control, sanitation and maintenance and walk the site when mosquitoes are actually active. Mark where density is highest and inspect the treatment tank covers, ventilation openings, plant saucers, gutters, ward flower vases, reserve water drums and every insect screen.
2. Fix the source and exclude them from the buildings
Repair the tank covers and fit insect mesh, remove every water-holding container, require ward vase water to be changed daily, fit lids to reserve drums, and repair all screening — then make screening a monthly maintenance checklist item.
3. Fog on schedule, and immediately on every dengue admission
Fog around the buildings twice a week through the rainy season and weekly in the dry, concentrating on the treatment tank, the landscaping around the inpatient building, the boundary, the kitchen and waste storage. Add an immediate application on every dengue admission, logging each one into the infection control system.
From someone who uses one
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The breeding sites healthcare teams most often miss
Flower vases brought by visiting relatives are the most common and most overlooked, because the water is typically changed only when the flowers wilt — which may be more than seven days — and those vases sit centimetres from the patient. The fix is making daily vase-water changes part of the ward routine.
Reserve water drums kept against supply interruptions are the second. Many community hospitals keep them in patient bathrooms and around the kitchen, usually uncovered. Requiring a properly fitting lid on every drum is a one-time measure with a permanent effect.
The sewage treatment tank and any ventilation sump are the most serious, particularly where covers are damaged or ventilation openings lack insect mesh. Make checking the covers and mesh a monthly item on the maintenance schedule.
Last are air-conditioner condensate trays and building gutters, which block with leaf litter from the landscaping around the wards. Gutters should be cleaned monthly, especially at hospitals with mature trees planted under a green hospital programme.
Mosquito management belongs inside the hospital's infection control system
The observation Dr Worapon stresses most is that every hospital has a strong infection control system for contact and airborne transmission — with protocols, named responsibility, surveillance and reporting — yet vector-borne disease has never been inside that same system.
Bringing mosquito management into infection control produces three important things: clear named responsibility; surveillance and auditable records; and regular review at meetings alongside every other indicator.
The protocols this hospital adopted and found effective were: a monthly breeding-site survey; scheduled fogging through the rainy season; immediate fogging on every dengue admission; and reporting dengue admissions against fogging activity at the infection control team meeting.
This documentation is also valuable at quality accreditation, because it demonstrates a systematic measure rather than a reaction to a problem — which assessors weigh far more heavily than simply owning equipment.
Frequently asked questions
Is fogging safe at a hospital with patients present?
Yes, when applied only outside the buildings and following the procedure: notify in advance, close ward windows and louvres during application, cover food and any equipment that needs it, and allow roughly 30 to 60 minutes before resuming normal ventilation.
Should we fog inside the wards?
In principle no, because of respiratory patients, elderly people and small children. Interior management should rely on repairing screening, removing water-holding containers and changing vase water daily. Concentrate fogging outdoors, where the mosquitoes reaching the wards originate.
When should we fog?
Around six in the evening, or before six in the morning, works best — matching Aedes activity in calm air, and coinciding with the periods of lowest outpatient traffic, so it disrupts services least.
How many machines does a facility of my size need?
A sub-district health promoting hospital is fine with one. A community hospital of 30 to 90 beds should have two, so a full pass finishes within an hour and there is a spare. General hospitals with multiple buildings should consider three or more.
How often should we fog?
Twice a week through the rainy season and weekly in the dry, plus an immediate application every time a dengue patient is admitted, to reduce the chance of mosquitoes acquiring the virus from that patient and biting others in the building.
Can hospital staff operate the machine?
Yes. Assign two or three maintenance staff as responsible operators and train them fully on mixing ratios, protective equipment and cleaning the machine after use, with every application logged into the infection control system.
Which budget category should this sit in?
The equipment category, referencing the standard equipment schedule, which already lists thermal foggers — so the reference price and acceptance inspection need no reinterpretation. Chemicals and fuel go under materials as usual.
What if the machine fails during the rainy season?
AIROFOG maintains a service centre and genuine parts in Thailand with technicians of more than 10 years' experience, so repairs are fast. Hospitals are advised to keep at least one spare machine and the common wear parts on site, because the rainy season is precisely when fogging cannot stop.
We are excellent at contact transmission — and we forgot the vectors
Dr Worapon's remark captures a gap many healthcare facilities share: we have strong systems for pathogens whose transmission route we can see clearly, and no equivalent system for disease carried by insects.
The principles are identical — eliminate the source, prevent access to the patient, and continuously reduce the vector load in the environment. What has to be added is only ready equipment and a schedule that is actually followed.
For a healthcare facility, preventing a patient admitted for one illness from acquiring another is not merely a quality indicator. It is the basic promise the hospital made to its community on the day it opened.
Talk to the World Health Disinfection team about a mosquito control system for your healthcare facility — machine selection, chemistry, schedule and staff training.
See the machine and pricing — click here
Call 065-556-6294 or add LINE @whd268
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