Seawater nasal wash to reduce symptom duration and viral load in COVID-19 and upper respiratory tract infections: a randomized controlled multicenter trial

The objective was to assess the efficacy of seawater nasal wash on symptom duration, intranasal viral load, household transmission in COVID-19 and URTIs. This prospective, randomized, controlled, multicentric, parallel study included 355 mild/moderate COVID-19 and URTI adults with rhinologic symptoms ≤ 48h. Active group performed 4-daily nasal washes with undiluted isotonic seawater versus control group (without nasal wash). Symptoms were self-assessed daily using the WURSS-21 questionnaire for 3 weeks. Viral load was measured by RT-PCR on nasopharyngeal swabs collected on Day 0, Day 5, Day 14 and Day 21. Digital droplet PCR was additionally performed for SARS-CoV-2. Overall COVID-19 subjects recovered earlier the ability to accomplish daily activities in the active group (– 1.6 day, p = 0.0487) with earlier improvement of taste (– 2 days, p = 0.0404). COVID-19 subjects with severe nasal symptoms at D0 showed the earliest resolution of anosmia (– 5.2 days, p = 0.0281), post-nasal drip (– 4.1 days, p = 0.0102), face pain/heaviness (– 4.5 days, p = 0.0078), headache (– 3.1 days, p = 0.0195), sore throat (– 3.3 days, p = 0.0319), dyspnea (– 3.1 days, p = 0.0195), chest congestion (– 2.8 days, p = 0.0386) and loss of appetite (– 4.5 days, p = 0.0186) with nasal wash. In URTIs subjects, an earlier resolution of rhinorrhea (– 3.5 days, p = 0.0370), post-nasal drip (– 3.7 days, p = 0.0378), and overall sickness (– 4.3 days, p = 0.0248) was reported with nasal wash. Evolution towards more severe COVID-19 was lower in active vs control, with earlier viral load reduction in youngest subjects (≥ 1.5log10 copies/10000 cells at Day 5: 88.9