Study: Air purifier use at daycare centres cut kids' sick days by a third (2023)

Original Article ↗ Hacker News Discussion ↗

Impact of Daycare Illness

  • Multiple parents report being sick very frequently when kids start daycare; some describe multi‑month cycles where the child gets sick late week, then the parents over the weekend.
  • Even with few symptomatic days for kids, adults often feel constantly mildly ill.
  • Commenters note large economic and productivity costs from parents caring for sick children and getting sick themselves.

Immune System “Training” Debate

  • One camp argues kids “need to get sick” to train immunity and worry that reducing infections is a “devil’s bargain.”
  • Others counter:
    • Exposure ≠ needing full‑blown illness; lower viral loads may act more like mild “natural vaccination.”
    • The hygiene hypothesis is described as tenuous and often misapplied; benefits are mainly from benign microbes, not pathogens.
    • Viruses can damage the immune system (e.g., measles immune amnesia, COVID‑related long‑term effects).
  • Several point out that a one‑third reduction in sick days still leaves plenty of exposure.

Air Purifiers, Ventilation, UV, CO₂

  • Many see HEPA/MERV filtration and increased air changes as clearly beneficial, aligning with other studies in schools/hospitals.
  • Some suggest improved ventilation (including HRV/ERV systems, outdoor daycare) may be better than, or complementary to, purifiers, especially for CO₂ control and cognition.
  • There is discussion of CO₂ as a proxy for ventilation and evidence that higher CO₂ can increase viral stability and reduce cognitive performance.
  • UV‑C and far‑UVC are seen as promising but technically tricky (correct wavelength, intensity, safety, bulb lifetime, plastic degradation, cost, certification).

Study Quality and Limitations

  • One commenter questions statistical significance and notes only two intervention units with mechanical ventilation; possible confounding from building differences and seasonal flu variation.
  • Others argue that a roughly 30% effect size is large enough to be meaningful if replicated.

Masks and Child Development

  • Question raised about combining masks with purifiers.
  • Some claim masks caused speech/language delays, especially for children not hearing the dominant language at home; others demand rigorous evidence and cite at least one study that did not support such harms.
  • Strong disagreement on whether anecdotes vs formal studies should be trusted, and whether masking costs outweigh infection risks (including long COVID).

Devices, DIY Solutions, and Practical Concerns

  • Frequent recommendations for:
    • Corsi–Rosenthal boxes (box fan + MERV 13 filters) as cheap, high‑performance options, though noisy and hard on fans.
    • Branded purifiers (e.g., IKEA, Austin Air) with attention to CADR and air changes per hour rather than marketing area claims.
  • Warnings:
    • Many commercial devices oversell coverage based on 1 ACH at max (loud) settings.
    • Poorly maintained filters can become moldy; some schools neglect filter replacement for years.
    • Air purifiers may increase airborne endotoxin in some contexts; better ventilation is suggested in that study.

Broader Implications and Policy

  • Some see this as analogous to historical shifts like adoption of surgical handwashing: indoor air quality (purifiers + ventilation) could substantially reduce population‑level illness.
  • Others caution against “destroy all microbes” thinking and emphasize ecological balance and antimicrobial stewardship.
  • There is frustration that lessons from COVID about airborne transmission, filtration, and ventilation have not been widely implemented in building codes, schools, and workplaces.