Air conditioning system usage and SARS-CoV-2 transmission dynamics in Iran

Recently, a group of 239 multidisciplinary scientists signed a document that urged the WHO and public health authorities to acknowledge the airborne transmission of SARS-CoV-2 [1]. Following this request, the WHO agreed that aerosol transmission potentially contributes to the pandemic, albeit close contact still remains the primary transmission route. This move urges the WHO to recommend precautionary actions against aerosol transmission and to improve guidelines for controlling viral spread. Studying transmission mechanics of SARS-CoV-2 are complicated and requires more knowledge and evidence concerning the infectivity of virus-laden aerosol [2]. However, clues from transmission events and current patterns at population level suggest incidences of aerosol transmission of SARS-CoV-2 [3].

Following the outbreak in China, Iran was overwhelmed by the SARS-CoV-2 epidemic in February 2020 and is among the most affected countries [4]. A lockdown was implemented and the Iranian state gradually lifted the restrictions after two months, encouraged by a drop in infected cases in April. However, from the beginning of May the numbers of new infections and mortality cases started to increase again.

Iran is a vast country with almost 83 million inhabitants living in 31 provinces. The country’s geographical location north of the Persian Gulf is influenced by meteorological dynamics that lead to almost 11 different climates [5]. The second wave of the epidemic started in five large provinces located in south and southwest that reported only few cases during the first wave. These regions have a temperate climate with maximum temperatures of 26 °C in February and March. Early May, the temperature steadily increases and requires people to turn on the air-conditioning systems at their homes and workplaces. Furthermore, people tend to stay inside to avoid the outside heat. Surprisingly, the second wave of the epidemic, which initiated in this region, coincided with increasing temperatures and air-conditioning usage. With a month delay, the same pattern is observed in other provinces that are currently experiencing the summer heat. Until now, the infection rate and mortality cases have skyrocketed and reached new records in daily death cases. At the time of writing, 27 out of 31 provinces are marked as red and orange zones that experience a massive wave of the infection.

Based on the current evidence and the pattern of the epidemic, we believe that cooling systems could contribute to the spread of SARS-CoV-2 in Iran. Besides creating air circulation in closed environments, these systems also reduce air humidity, which promotes the spread of virus-laden micro-droplets [6]. Accordingly, we urgently advise health policy makers to regard the role of ventilation systems in the guidelines for controlling the epidemic.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.