Stronger susceptibilities to air pollutants of influenza A than B were identified in subtropical Shenzhen, China

Air pollution was indicated to be a key factor contributing to the aggressive spread of influenza viruses, whereas uncertainty still exists regarding to whether distinctions exist between influenza subtypes. Our study quantified the impact of five air pollutants on influenza subtype outbreaks in Shenzhen, China, a densely populated and highly urbanized megacity. Daily influenza outbreak data of laboratory-confirmed positive cases were obtained from the Shenzhen CDC, from May 1, 2013 to Dec 31, 2015. Concentrations of nitrogen dioxide (NO₂), sulfur dioxide (SO₂), particulate matters ≤2.5 μm (PM_2.5), particulate matters ≤10 μm (PM₁₀), and ozone (O₃), were retrieved from the 18 national monitoring stations. The generalized additive model (GAM) and distributed lag non-linear model (DLNM) were used to calculate the concentration-response relationships between environmental inducers and outbreak epidemics, respectively for influenza A (Flu-A) and B (Flu-B). There were 1687 positive specimens were confirmed during the study period. The cold season was restricted from Nov. 4th to Apr. 20th, covering all seasons other than the long-lasting summer. Relatively heavy fine particle matter (PM_2.5) and NO₂ pollution was observed in cold months, with mean concentrations of 46.06 μg/m³ and 40.03 μg/m³, respectively. Time-series analysis indicated that high concentrations of NO₂, PM_2.5, PM₁₀, and O₃ were associated with more influenza outbreaks at short lag periods (0-5 d). Although more Flu-B (679 cases) epidemics occurred than Flu-A (382 cases) in the cold season, Flu-A generally showed higher susceptibility to air pollutants. A 10 μg/m³ increment in concentrations of PM_2.5, PM₁₀, and O₃ at lag 04, was associated with a 2.103 (95%CI: 1.528-2.893), 1.618 (95%CI: 1.311-1.996), and 1.569 (95%CI: 1.214-2.028) of the relative risk (RR) of Flu-A, respectively. A 5 μg/m³ increase in NO₂ was associated with higher risk of Flu-A at lag 03 (RR = 1.646, 95%CI: 1.295-2.092) and of Flu-B at lag 04 (RR = 1.319, 95%CI: 1.095-1.588). Nevertheless, barely significant effect of particulate matters (PM_2.5, PM₁₀) on Flu-B and SO₂ on both subtypes was detected. Further, the effect estimates of NO₂ increased for both subtypes when coexisting with other pollutants. This study provides evidence that declining concentrations of main pollutants including NO₂, O₃, and particulate matters, could substantially decrease influenza risk in subtropical Shenzhen, especially for influenza A.

Association between meteorological factors and the epidemics of influenza (sub)types in a subtropical basin of Southwest China

BACKGROUND

The effects of climatic conditions on the prevalence of individual influenza (sub)types are not well understood in the subtropics. This study aims to evaluate the associations between meteorological factors and seasonal epidemics of A(H3N2), A(H1N1)pdm09, and type B influenza viruses, as well as to estimate the interactions between climatic variables in a subtropical basin region.

METHODS

The seasonality of influenza (sub)types during 2010-2019 were characterized in Chengdu Plain Economic Zone, a densely populated and highly humid plain area in Sichuan Basin in subtropical Southwest China. Generalized additive models were adopted to assess the independent exposure-response relationship between meteorological variables and influenza prevalence. The interactions of meteorological variables were further estimated using bivariate response surface models and strata models.

RESULTS

Our analyses indicated that the temperature, relative humidity, and absolute humidity have exhibited a major influence on influenza infection in Chengdu Plain Economic Zone. Low temperature was shown to promote the prevalence of A(H1N1)pdm09 and type B in winter-spring days at all levels of relative humidity. High risk of A(H3N2) infections was observed at low temperature or high temperature, and at higher relative humidity. Moreover, absolute humidity decreased or increased influenza (sub)type infections within different ranges.

CONCLUSIONS

This study found different nonlinear relationships between meteorological factors and the seasonality of influenza (sub)types, as well as significant interactive effects between climatic variables, contributing to the research on the climate drivers of influenza prevalence in warm-humid basin regions in the subtropics.

Demographic, clinical, and virological characteristics of patients with a laboratory-confirmed diagnosis of influenza during three consecutive seasons, 2015/2016-2017/18, in the Islamic Republic of Iran

BACKGROUND

There are minimal data on the differences in demographics, clinical presentations and outcomes for patients with different types and sub-types of influenza in the Middle East.

OBJECTIVES

To use population-based data from Iran to investigate factors associated with unfavorable disease outcome.

STUDY DESIGN

Clinical data were compiled from the Iranian Ministry of Health for patients of all ages who fulfilled the severe acute respiratory infections (SARI) definition according to World Health Organization criteriatested for any reason and found to have and had laboratory proven influenza September 21, 2015 through March 20, 2018. Pulmonary, cardiac, renal, hematologic and neurologic complications were recorded. Results were compared by type, age, gender and health status. Multivariate analysis was used to analyze risk factors for complications and death.

RESULTS

Of 11,080 enrolled patients, 10,046 (90.7 %) were inpatients, 2254 (20.4 %) were children, 8403 (75.8 %) had influenza A, 2599 (23.5 %) had influenza B, and 78 (0.7 %) had unidentified types. Fever was less common in older patients (OR 0.99; 95 % CI 0.98-0.99, p < 0.001 and in those with comorbidity (OR 0.87; 95 % CI 0.77-0.97, p = 0.013). Although the rate of complications was lower with A(H1N1) pdm09 influenza than with A(H3N2) infection (12.8 % versus 15.6 %, p = 0.001), the mortality rate was higher (7.0 % versus 3.0 %, p < 0.001). Complications occurred more often during late versus early influenza season (OR 1.22; 95 % CI 1.08-1.37, p = 0.002). Patients with type B influenza (OR 0.85; 95 % CI 0.74-0.98, p = 0.025), or who presented with sore throat (OR 0.74; 95 % CI 0.65-0.84, p < 0.001) were less likely to develop complications. The risk of developing complications was increased in patients who had chronic heart disease (OR 1.51; 95 % CI 1.29-1.76, p < 0.001), chronic pulmonary disease (OR 1.62; 95 % CI 1.37-1.91, p < 0.001), diabetes (OR 1.24; 95 % CI 1.03-1.50, p = 022), or epilepsy (OR 1.55; 95 % CI 1.17-2.05). Older age and male gender increased the risk of death but not of complications.

CONCLUSIONS

The clinical features, complications and outcomes of influenza vary by age and by viral type and sub-type. Comorbidites appear to be more important than age in predicting complications.