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Point & Counterpoint: HEPA filter-based air purifiers in hospitals

A medical doctor and a biomedical engineer agree and disagree about the role of such air purifiers in the healthcare setting, putting forth the strengths and limitations of all solutions.

Dr Sarthak Rastogi, practising pulmonologist and consultant at Holy Family Hospital and SL Raheja Hospital, Mumbai:

HVAC systems and Covid transmission

The SARS-CoV-2 virus particle is only 0.1 micrometer in diameter. It can escape most efficient filters but it is excreted by humans through aerosol generation: either respiratory droplets or droplet nuclei. These aerosols-carrying viruses, by virtue of also having mucus excretions, make the size of the aerosols much larger than the size of the virus. This makes it easier for the filters in the HVAC system to trap the virus with better efficacy.

The issue of the virus being transmitted by the HVAC system is a difficult concept to prove. Viral RNA isolated from the HVAC system is not sufficient to prove that there is infection transmission. There have been studies demonstrating the live virus but the quantity recorded appears to be insufficient for infection. HVAC maintenance has become a challenge in the Covid ICUs, as most of them are running at full capacity, without breaks and see prolonged stays with critical conditions.

The role of HEPA filters

As far as SARS-CoV-2 is concerned, the only air purifiers that seem to be reasonably effective are HEPA filter-based purifiers, which can be portable ones too. Though expensive, they can be stationed where healthcare staff are gathered in the Covid wards, and work better with universal masking. They can be placed in areas with high risk patients and those having improper outdoor air/natural ventilation, such as chemotherapy units or dialysis units or where other immunosuppressed patients are housed in non-Covid settings.

However, limited scientific evidence is available. Wherever natural light and ventilation is secured, air purifiers can be of very limited value. In Covid settings, in ICUs with patients with respiratory failure on non-invasive ventilation, those undergoing procedures of the airway like intubation, bronchoscopy and tracheostomy, which are the highest aerosol-generating procedures, the HEPA filter-based purifier may be of some value.

In OPDs, it will be cost-effective and easier to install fans and open up windows; that will dilute the indoor air and decrease the chance of infections.

As most patients do ask about the role of air purifiers for their home, in the pandemic, this question has come but too often. Acceptance should be good, although many hospitals have not installed such devices, so it is difficult to foresee the acceptance issues that may arise.

Dilip Patil, Managing Partner, Trivector Biomed LLP:

HEPA filters are not recommended

Neither do HEPA filters kill microorganisms nor do they eliminate them; they just trap pathogens. If these filters are not replaced regularly, bacterial colonisation of filters may happen. HEPA filter-based air purifiers are mostly ionisers, which spray positive or negative ions which agglomerate with the microorganisms in the room and settle on surfaces and walls. The byproducts of ionisation (like ozone) may be harmful for human beings and are not recommended to be used in critical health care settings. HEPA filter based air-purifiers also consume more electricity and are comparatively noisy.

The alternative: Novaerus ‘NanoStrike’ technology

This is based on ultra-low energy cold plasma that destroys the pathogens which pass through the plasma field in milliseconds at the DNA/RNA level. Disinfection happens inside the device and safe medical grade air is continuously delivered into the room. These eco-friendly devices are portable, silent and consume very less electricity. There are no filters or lamps to be replaced. They need almost zero maintenance, making them the air-disinfection devices with the lowest life-cycle cost for the end user.

What makes them safe for hospitals?

Unlike other air-purifiers which use ionization, photocatalytic oxidation, UV lights or chemicals, which generate harmful by-products detrimental to human health, Novaerus devices can be used all the time in human occupied rooms in the breathing zone, without any side-effects. The efficacy and safety of Novaerus devices is validated by independent international institutes and they eliminate the pathogens like SARS-CoV-2 up to 99.997% in a short time.

Usefulness in healthcare 

Thousands of these units are being used all over the world in various healthcare settings, including the Karolinska Institute in Sweden (which confers the Nobel Prize for Medicine). In India, we have hundreds of units installed and protecting health-care workers and patients in Covid ICUs, NICUs, diagnostic labs, IVF labs and veterinary labs. Pulmonology and chest OPDs, X-ray rooms and TB wards are the places where Novaerus devices would be most useful.


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