annually , more than 2.5 million muslims from about 140 countries go on the hajj pilgrimage , which is the largest mass gathering in the world .
the presence of such a vast number of people in the holy places , especially in the cities of mecca and medina , and the massive pilgrim crowds in certain places at certain times , causes infectious diseases to spread more easily .
racial , cultural and health differences , as well as the level of access to health , medical and welfare services at the time of stay in these places are important factors that increase the risk of communicable diseases
. both , viral or bacterial respiratory tract infections are very common among pilgrims in all age and sex groups , and is regarded as the most common disease among pilgrims in some reports .
some studies have also reported the prevalence of different types of these infections up to 85.3% . to prevent these infections ,
some preventive measures have been recommended for the pilgrims , such as mandatory injection of tetravalent meningococcal meningitis vaccine , recommendation to inject seasonal flu vaccine , and using surgical masks . on the other hand ,
each country plans and implements some specific measures to prevent and control these diseases among pilgrims .
more than 100,000 iranians in about 600 caravans undertook the hajj in 2010 . according to the current policies of the hajj medical center of iran , before traveling any caravan
common diseases detected among pilgrims are treated in the caravan itself , or referred to the medical center , if needed .
the reports show conflicting results about the effects of preventive measures for respiratory tract infections and in fact , a precise study on the effects of each one of these preventive measures has been rarely done .
this research is trying to examine the effects of general preventive measures on respiratory tract infections through a nested case - control study , which is more precise design than ordinary case - control studies .
we used nested case - control design , which is based on risk set sampling .
the studied cohort consist two caravans ( 338 pilgrims ) , one of which was the first to enter mecca , and the other the first to enter medina .
the outcome of this study was all types of respiratory tract infections other than the common cold including tonsillitis , pharyngitis , laryngitis , sinusitis , otitis media , bronchitis , pneumonia and influenza .
as soon as any patient in the caravans was identified , a data collection form was completed for that individual .
considering that the level of presence in saudi arabia and the amount of contact with all types of viruses and bacteria are regarded as risk , on the day of identifying each patient , two pilgrims in the same caravan were randomly selected as control group .
each control pilgrim was not affected by the mentioned outcome at the time of investigation , although these pilgrims may be enrolled as a case in future days .
every pilgrim who become ill with studied disease and had consent to participate , was enrolled in the study .
all pilgrims who did not get the studied disease at time of selection and had consent to participate , could be enrolled as controls .
body mass index ( bmi ) is calculated by dividing the weight in kilograms to height square in meter . if another patient with studied disease existed in the same room then the pilgrim considered as having  room contacty  .
if the pilgrims used face masks in crowding , even occasionally were considered as  using face mask  .
pilgrims considered as vaccinated against influenza if they vaccinated by this vaccine since two years before traveling to saudi arabia .
pilgrims , who washed their mouth and throat with salt water at least once a day , were considered as having  salt water gargling  .
pilgrims with a past history of at least one systemic diseases including asthma , diabetes mellitus , hypertension , copd and cardiovascular diseases were considered as having  systemic diseases  . present or past smoker with any type and amount of smoking were considered as smokers .
if the pilgrims used personal prayer carpet in holy places were considered as  using personal prayer carpet  .
the effect of each preventive measure on the occurrence of respiratory tract infections was studied through a univariable model . at the next stage , all variables which were significant in the first stage ( p < 0.2 ) , were entered into the multiple models , and the adjusted odds ratio was obtained for each one of the variables .
we used nested case - control design , which is based on risk set sampling .
the studied cohort consist two caravans ( 338 pilgrims ) , one of which was the first to enter mecca , and the other the first to enter medina .
the outcome of this study was all types of respiratory tract infections other than the common cold including tonsillitis , pharyngitis , laryngitis , sinusitis , otitis media , bronchitis , pneumonia and influenza .
as soon as any patient in the caravans was identified , a data collection form was completed for that individual .
considering that the level of presence in saudi arabia and the amount of contact with all types of viruses and bacteria are regarded as risk , on the day of identifying each patient , two pilgrims in the same caravan were randomly selected as control group .
each control pilgrim was not affected by the mentioned outcome at the time of investigation , although these pilgrims may be enrolled as a case in future days .
every pilgrim who become ill with studied disease and had consent to participate , was enrolled in the study .
all pilgrims who did not get the studied disease at time of selection and had consent to participate , could be enrolled as controls .
body mass index ( bmi ) is calculated by dividing the weight in kilograms to height square in meter . if another patient with studied disease existed in the same room then the pilgrim considered as having  room contacty  .
if the pilgrims used face masks in crowding , even occasionally were considered as  using face mask  .
pilgrims considered as vaccinated against influenza if they vaccinated by this vaccine since two years before traveling to saudi arabia .
pilgrims , who washed their mouth and throat with salt water at least once a day , were considered as having  salt water gargling  .
pilgrims with a past history of at least one systemic diseases including asthma , diabetes mellitus , hypertension , copd and cardiovascular diseases were considered as having  systemic diseases  . present or past smoker with any type and amount of smoking were considered as smokers .
if the pilgrims used personal prayer carpet in holy places were considered as  using personal prayer carpet  .
the effect of each preventive measure on the occurrence of respiratory tract infections was studied through a univariable model . at the next stage , all variables which were significant in the first stage ( p < 0.2 ) , were entered into the multiple models , and the adjusted odds ratio was obtained for each one of the variables .
during the hajj pilgrimage , 32 people ( 9.5% ) of the cohort ( 338 pilgrims ) were affected by respiratory tract infections . according to the explained method
description of cases and controls , in terms of age , sex , education and other factors which influence the incidence of respiratory tract infections , are presented in table 1 .
distribution of factors affecting respiratory tract infections in hajj pilgrims , 2010 sixty nine percent of the patients were treated with symptomatic treatment and oral antibiotics , and 27.5% required treatment through intravenous antibiotics as well .
in addition , 79.3% of the patients fully recovered through the treatment administered in the caravan , but 17.2% were referred to the hajj medical center , and finally 3.4% of the total patients were hospitalized in that center .
univariable logistic regression analysis showed that among the variables studied , only gargling with salt water , presence of other patients in the room , age and level of education , have p < 0.2 and can be associated with respiratory tract infections . among these variables ,
gargling with salt water with or = 2.4 and p = 0.08 had the strongest relationship [ table 2 ] .
the role of protective measures and other individual factors on respiratory tract infections among hajj pilgrims , 2010 the multivariable logistic regression model showed that none of the factors listed above were significantly associated with the outcome being studied .
for example , presence of the other patient in the room increases the risk of outcome by 2.67 times , but this effect is not significant , according to the confidence intervals of or [ table 2 ] .
the results also showed that the current preventive measures including wearing face masks , seasonal flu vaccination , and use of personal prayer carpet were not effective enough in the prevention of these infections .
however , the seasonal flu vaccination has been recommended , especially in high - risk individuals or those over 65 years of age .
the influenza vaccine has been proved by other researchers to have no effect in the prevention of respiratory infections , and it has even been seen that the use of seasonal influenza vaccine prolongs the period of sore throat .
however , methodological problems of the studies and the applied methods , including laboratory or demographic studies , should be considered when comparing these results .
it should also be noted that recommendations to take a seasonal influenza vaccine is due to its preventive effect on the incidence of flu and reduction of the risk of pandemic swine flu .
other studies , like the results of this study , have shown that wearing face masks has no effect on respiratory infections .
although the cdc does not recommend wearing it , the saudi ministry of health recommends that pilgrims wear face masks .
the recommendation to wear masks is probably because of its role in the prevention of tuberculosis , which has not been studied among the pilgrims .
the effect of using a personal prayer carpet has not been studied in other reports .
probably , the close contact of the pilgrims with each other , and their presence in crowded places are the main causes for transmission of respiratory infections , so it hinders a possible protective role played by the personal prayer carpet .
although , the effect of this action on the prevention of respiratory infections was not significant in the multiple logistic model , it seems that the reason for it is the relatively small sample size in the study .
in other words , through studies with a larger sample size , it may be concluded that lack of gargling with salt water increases the risk of respiratory infections by 2.3 times .
similarly , it can be said that staying with other patients in the same room increases the risk of respiratory infections by 2.67 times . as can be seen in table 2 , factors such as age , sex , level of education , area of the room , smoking , systemic diseases , obesity , and the average daily hours of gathering together in the holy places have no effect on respiratory tract infections .
in other words , any age and sex group with different individual conditions is likely to get exposed to viral and bacterial causes of these infections . as mentioned above , the relatively small sample size is one of the limitations of this study .
an increase in the sample size would make it possible to study the role of factors associated with respiratory infections in any of the holy places ( mecca , medina , mina , etc . ) . in this study ,
the cases were of those who were diagnosed clinically by a caravan physician . if the rapid test diagnosis is applied along with the acceptable sensitivity and specificity to diagnose cases , the accuracy of the study will increase .
flu vaccinations wearing face masks , personal prayer carpet , smoking , obesity , etc . , do not affect the incidence of respiratory infections during the hajj , and if this study is to be undertaken with a larger sample size , according to the appropriate selected methodology , some evidence will be obtained showing the prophylactic effect of gargling with salt water in the prevention of these infections .
 background : respiratory tract infections are very common among the hajj pilgrims . some preventive measures including influenza vaccination , using face mask and salt water gargling have been considered to control these infections and the reports show conflicting results about the effects of each one of these measures . this study is trying to assess the effects of these recommendations on respiratory tract infections.methods:according to nested case - control design , in a cohort consisting of 338 iranian pilgrims , the outcome examined , was all types of respiratory tract infections other than common colds . with occurrence of any patient in convoy , data collection form was completed for that person . on the same day , 
 two people were randomly selected as control group from among pilgrims who have not affected so far.results:during hajj , 32 pilgrims ( 9.5% ) were affected by respiratory tract infections other than common colds . in univariable logistic regression analysis , salt water gargling ( or = 2.4 , p = 0.08 ) , existence of other patient in the room ( or = 2.14 , p = 0.19 ) , age over 60 years ( or = 1.84 , 
 p = 0.15 ) and the education more than or equal to 3 years ( or = 1.93 , p = 0.16 ) were effective in the respiratory tract infections ( p < 0.2 ) . 
 however , multivariable logistic regression analysis showed that none of the above mentioned factors are significantly associated with these infections.conclusions:this study showed that measures such as seasonal influenza vaccination , use of face masks and personal prayer carpet have no effect on the incidence of respiratory tract infections . 
 however , washing throat and mouth with salt water can be considered the most effective preventive measures . 
INTRODUCTION
METHODS
Design
Definition and measures
Statistical analysis
RESULTS
DISCUSSION
CONCLUSIONS