Background: To assess the concurrent and predictive validity of the Nasal Mucus Index (NMI), a novel measurement of acute respiratory infection (ARI) severity.
Objective: ARI, including the common cold and influenza, imposes a great burden on individuals and society. Previous research has attempted to assess the severity of ARI with self-reported and laboratory-based measurements. Self-reported measurements may introduce bias. Laboratory-based metrics are often expensive. Therefore, there is a need for non-self-reported, affordable, and validated ARI severity tests.
Methods: Participants (N = 719) with an ARI episode underwent nasal lavage on days 1 and 3. The samples were visually assessed for the amount of mucus present in the sample and were given a subsequent NMI score. Collected samples were further assessed for interleukin (IL) 8 values (in pg/mL) and polymorphonuclear neutrophils (PMN) per high-power field. The participants rated episode severity and nasal symptoms daily by using the validated Wisconsin Upper Respiratory Symptom Survey-21 (WURSS-21). A subset of nasal symptoms was used as an additional comparator. NMI scores were compared with same-day IL-8 level, PMN count, and WURSS-21 scores for concurrent validation purposes by using the Spearman ρ as the index of correlation. NMI scores were correlated with overall episode severity measurements to assess predictive validity. Overall episode severity was measured as the WURSS-21 area under the curve, nasal symptoms area under the curve, and episode duration.
Results: The NMI score correlated significantly with the same-day IL-8 level (ρ = 0.443, p < 0.001), PMN count (ρ = 0.498, p < 0.001), WURSS-21 score (ρ = 0.098, p = 0.004), and nasal symptom score (ρ = 0.162, p < 0.001). No significant predictive correlations were found.
Conclusion: Associations with inflammatory biomarkers and self-reported severity measurements provided evidence of concurrent validity for the novel NMI score. The NMI can be used in future research as a simple, inexpensive, non-self-reported indicator of ARI severity.