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Heat and cold-related morbidity risk in north-east of Iran: a time-stratified case crossover design


This study aimed to estimate morbidity risk/number attributed to air extreme temperatures using time-stratified case crossover study and distributed lag non-linear model in a region of Iran during 2015–2019. A time-stratified case crossover design based on aggregated exposure data was used in this study. In order to have no overlap bias in the estimations, a fixed and disjointed window by using 1-month strata was used in the design. A conditional Poisson regression model allowing for over dispersion (Quasi-Poisson) was applied into Distributed Lag Non-linear Model (DLNM). Different approaches were applied to estimate Optimum Temperature (OT). In the model, the interaction effect between temperature and humidity was assessed to see if the impact of heat or cold on Hospital Admissions (HAs) are different between different levels of humidity. The cumulative effect of heat during 21 days was not significant and it was the cold that had significant cumulative adverse effect on all groups. While the number of HAs attributed to any ranges of heat, including medium, high, extreme, and even all values were negligible, but a large number was attributable to cold values; about 10000 HAs were attributable to all values of cold temperature, of which about 9000 were attributed to medium range and about 1000 and less than 500 were attributed to high and extreme values of cold, respectively. This study highlights the need for interventions in cold seasons by policymakers. The results inform researchers as well as policy makers to address both men and women and elderly when any plan or preventive program is developed in the area under study.

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Data availability

The dataset analyzed during the current study is not publicly available due to ethical concerns but are available from the corresponding author on reasonable request.


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This study was financially supported by North Khorasan University of Medical Sciences. The authors thank the Deputy of Health of North Khorasan University of Medical Sciences for providing the data.

Code availability

The R codes are available under request from corresponding author


This work was supported by the Deputy of research and technology, North Khorasan University of Medical Sciences [Grant No. 990175].

Author information

Authors and Affiliations



Hamid Reza Shoraka: project administration, conceptualization; data curation; funding acquisition, roles/writing - original draft; writing—review & editing.

Omid Aboubakri: formal analysis; investigation; methodology; project administration; resources; software; supervision; roles/writing—original draft; writing—review & editing.

Joan Ballester: methodology; validation; writing—review &editing.

Rahim Sharafkhani: writing—review & editing, investigation

Corresponding author

Correspondence to Omid Aboubakri.

Ethics declarations

Ethics approval

The proposal for this study was approved by the Ethics Committee of North Khorasan University of Medical Sciences. Ethics code is IR.NKUMS.REC.1400.032

Consent to participate

The data from hospital was collected with no personal identification.

Consent for publication

Not applicable

Competing interests

The authors declare no competing interests.

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Responsible Editor: Lotfi Aleya

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Shoraka, .R., Aboubakri, O., Ballester, J. et al. Heat and cold-related morbidity risk in north-east of Iran: a time-stratified case crossover design. Environ Sci Pollut Res 29, 2664–2671 (2022).

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  • Hospital admissions,
  • Cold,
  • Heat,
  • Attributable risk,
  • Case crossover,
  • Iran