acute respiratory infections ( aris ) are important under - five morbidities causing lots of discomfort , frequent visits to a healthcare provider , admission to an indoor facility , and even mortality [ 1 , 2 ] . india 's reproductive and child health programme has components for the prevention and control of ari since 1992 . aris , however , still continue to be the single largest contributor of childhood morbidity and mortality with estimated 35 episodes every year , 4 million pneumonias , and 1 million deaths [ 46 ] . estimates also indicate that 3050% of opd attendance and 2040% of hospital admissions may be attributed to ari and pneumonia . for a disease of such magnitude and severity , it is important that all aspects of its epidemiology have to be known . yet unfortunately , there are few studies reporting the detailed epidemiology of aris . of the few studies that exist , very few studies have been conducted in peri - urban communities and fewer involved active surveillance done prospectively by qualified and trained health practitioners . besides , most studies are 1 to 2 decades old [ 817 ] . in view of above , a prospective study to find out the current epidemiology of aris among infants and toddlers , the most affected age group , was planned . we report here the incidence , prevalence , clinical pattern , severity , seasonal pattern , and gender differences . this community - based follow - up study was conducted in 2011 - 12 at mehrauli , a peri - urban field practice area attached to the department of community medicine of a tertiary care teaching hospital of new delhi . optimum sample size was worked out to be 106 children or 5512 child - weeks of exposure . owing to logistics needed for the fortnightly follow - up , the study was restricted to one of the wards selected randomly ( ward 4 ) . cut - off age for enrollment of children was kept as 24 months so as to ensure a follow - up of 12 months before child ceased to be toddler . the only inclusion criterion was parents ' willingness to let their children participate , while exclusion criteria were two - fold : ( i ) child suffering from any chronic / severe illness and ( ii ) family of child not a permanent resident of ward 4 . our sampling frame was constituted of 264 under - two children identified through a house - to - house survey one month prior to the study . of these , 23 were not eligible for being included in the study ( 1 had thalassemia , 1 had nephrotic syndrome , 1 had very low birth weight , and 20 were temporary residents ) . three parents refused to let their wards participate and were replaced by another eligible child residing closest to the refusal . history regarding presence of ari currently or in the past fortnight was elicited from a responsible caregiver and recorded on mics proforma of unicef . all children , whether or not their parents reported a current / past bout of ari , were assessed clinically by a qualified trained medical practitioner on the designated day . additional information on type of ari , its severity , other accompanying symptoms , and so forth was assessed and recorded in a separate interview schedule validated by a faculty from paediatrics department . background information on the physical , biological , and sociodemographic environment as well as the general health status of the child was noted . in context of physical environment , overcrowding , indoor air pollution , environmental tobacco smoke , and so forth history of breast feeding , immunization , and exposure to ari from siblings was assessed as part of the biological environment . education , occupation , income , and social class formed the main stay of our sociodemographic assessment . information collected on interview schedules was cross - checked for completeness and correctness by supervisors and a database was created using microsoft excel software . incidence density of all aris has been described in terms of mean number of episodes per 100 child - weeks of exposure . chi - square test has been used to detect statistical significance at 5% level of significance . a total of 2752 contacts were made with 67 boys and 39 girls at their residences . one enrolled subject went out of town for 2 months , thus reducing our observation period by 8 child - weeks to 5503 child - weeks of exposure . four - fifth of study subjects were from middle income group and the remaining from high income families . a little over 5% of the mothers were illiterate and 32.1% had less than five years of schooling . close to half of the subjects lived in overcrowded ( 47% ) or ill - ventilated ( 21% ) houses , and 14% of households did not have a separate kitchen and 18% were using biomass fuels in addition to liquefied petroleum gas ( lpg ) . besides , 45% of study subjects were exposed to environmental tobacco smoke ( ets ) . one - fourth of subjects were having mild - to - moderate protein energy malnutrition ( pem ) . health assessment based on history as well as physical examination revealed that ari was the commonest illness ( 437 episodes in 105 children ) followed by diarrhea ( 253 episodes in 85 individuals ) and fever ( 69 episodes in 48 individuals ) . prevalence of ari , diarrhea , and fever was thus found to be 34.5 , 19.9 , and 5.4 percent , respectively . only 1 child did not seem to suffer from any type of ari during the study period , 105 ( 99.1% ) children suffered from no pneumonia , cough , and cold ( alone or in combination with other types of ari ) , 38 ( 35.8% ) had pneumonia , and 5 ( 4.7% ) had otitis media . of the 437 ari episodes , 390 ( 89.2% ) affected the upper respiratory tract only , 47 ( 10.7% ) were pneumonias , and 5 ( 1.1% ) were otitis media . out of those children suffering from ari , proportions of children suffering from 1 to 3 , 4 to 5 , and 6 to 7 episodes of ari were 35.2 , 45.7 , and 19.1 percent , respectively . of the 38 children who suffered from pneumonia , 9 ( 23.7% ) had two episodes . the mean duration of uri was 6.16 days ( range : 414 days ) as compared to 11.65 days for lri ( range : 719 days ) . the overall incidence of ari ( all types ) was found to be 7.9 episodes/100 child - weeks of exposure ; incidence was higher in infancy ( 9.4 episodes/100 child - weeks ) as compared to toddlers ( 7.0 episodes / per 100 child - weeks ) . incidence of pneumonia was found to be 0.8 episodes/100 child - weeks ( 1.1 in infancy and 0.7 in toddlers ) . highest incidence of pneumonia was seen in children less than 2 months of age ( 1.7 episodes/100 child - weeks ) . incidence of no pneumonia , cough , and cold was nearly constant throughout infancy , decreasing in the second and third years of life ( lowest incidence of 3.3 episodes/100 child - weeks seen in children of 3036 months ) . the incidence of pneumonia was one - tenth that of ari and that of severe pneumonia or otitis media was roughly one - tenth that of pneumonia . no case of otitis media was seen in infants less than 2 months of age and none of the toddlers were found to suffer from severe pneumonia . incidence of pneumonia was , however , noted to be higher in boys ( 0.9 episodes/100 child - weeks ) as compared to girls ( 0.6 episodes/100 child - weeks ) . similar pattern was seen for severe pneumonias also ( 0.1 for boys as compared to 0.05 for girls ) . in contrast , the incidence of  no pneumonia , cold , and cough  as well as otitis media was found to be higher in girls . figure 1 shows the monthly incidence of  ari  ( all types including otitis media ) ,  no pneumonia , cough , and cold ,   pneumonia ,  and  otitis media  among infants and toddlers . the monthly incidence of aris ranged from a low of 5.2 episodes/100 child - weeks ( in may ) to a high of 15.8 ( in february ) . two peaks were seen with the more prominent peak falling in the month of february which coincided with spring season . incidence of pneumonia also showed a fluctuation , ranging from a low of 0.2 episodes/100 child - weeks in may to a high of 1.5 episodes/100 child - weeks in march ( visible as a peak ) and november ( visible as a less prominent plateau ) . this community - based prospective study conducted in delhi provides information on risk of developing ari in tropical peri - urban settings of developing countries . our study had a very low attrition rate ( 1.6% ) all of which was attributable to social migrations . we believe that the child - weeks lost to attrition were not systematically different from those included for analysis . besides , though living standards of delhi are better than those in other areas of india as a whole , owing to the lack of primary health care system and higher levels of pollution ( as is the case in most urban areas ) , there is likely to be a balancing effect , thereby making our estimates representative of similar peri - urban areas . prevalence of ari in this study stood at 34.3% as compared to 19.9% and 5.4% for diarrhea and fever , respectively . the relative importance of ari as a cause of disease , not just mortality , in young children was , hence , reestablished . nfhs 3   reported that 5.8% of children under 5 years suffered from ari ( cough plus short , rapid breathing ) during the 2-week - period preceding the survey . the difference is due to variations in methodology ( nfhs used a one - time survey technique conducted by nonmedical personnel and no examination was involved ) . have also documented ari to be a major cause of morbidity among rural children with prevalence rates of 35.4 per hundred days of observation . the bangladesh study , however , reports that nearly 9% of their study subjects did not suffer from any ari episode during the 12-month study period which is a highly desirable situation compared to only 0.9% in our case . our findings are also in concurrence with those reported by koch et al . in their greenland study . annual incidence of ari in this study was 4.1 episodes / child ( 7.9 epi/100 child - wks ) . acharya et al .   in 2003 found ari incidence of 6.4 episodes per child per year . reported 3.7 episodes of ari among under - five children of wardha , maharashtra in 1996 , while awasthi and pande   from lucknow have reported the lowest ari incidence of 1.67 episodes . studies from neighbouring bangladesh   too have reported annual ari incidence to be 5.5 episodes per child . although our observations fall within the range of what others have reported , still it would be the best not to compare our findings with that of others for the following three reasons : ( i ) while most workers have studied children up to 5 years of age , we focused on infants and toddlers exclusively , the age which is most affected by aris ; ( ii ) some studies were conducted in part of the year only and not a full calendar year ; and ( iii ) the questions used to estimate ari might have been different in different studies . we found annual pneumonia incidence to be 0.44 episodes / child ( 0.85 episodes/100 child - weeks ) which is much higher than that reported by most workers and agencies . for example , the joint unicef - who document on pneumonia of 2006   reports an incidence of 0.30 episodes / child / year for india as a whole and rudan et al . singh and nayar   have reported an annual incidence of pneumonia among under - five children of wardha ( maharashtra ) in 1996 to be 0.07 episodes / child , while awasthi and pande   found pneumonia incidence of 0.09 per child per year in lucknow , up . , however , report a higher pneumonia incidence of 0.52 episodes per child per year from rural udupi in karnataka . in bangladesh   much lower incidence of acute lower respiratory infections ( i.e. , pneumonia ) was reported ( 0.23 per child per year ) . the reason for the high prevalence of aris and higher incidence of pneumonia in the present study could be ( i ) higher levels of air pollution , ( ii ) overcrowded and ill - ventilated living conditions , and ( iii ) lack of a primary health care mechanism . the latter has also been documented in pakistan by singh and nayar which records that 13% of  no pneumonia  is likely to turn into pneumonia , and a significant proportion of these would be prevented if appropriate care is available . we found 10.1% of all ari episodes to be pneumonia and 0.7% to be severe pneumonia . awasthi and pande   found 10% of  respiratory disease  to be  pneumonia  in lucknow , while acharya et al .   reported 8.7% to be pneumonia and 0.5% to be severe pneumonia in udupi , karnataka . in contrast , 4% of ari episodes were reported to be pneumonia in bangladesh . on the other hand , incidence of otitis media in the current study ( 0.01% ) is much lower than the 30% estimated incidence among ari cases as reported by simoes et al .   for developing countries . the difference could be due to difficulty in making an assessment of otitis media which requires otoscopy , a procedure we could not conduct in field conditions . the mean duration of no pneumonia , cough , and cold was 6.16 days as compared to 11.65 days for pneumonia in our study . the bangladesh study   reported that 46 percent of uri and 65 percent of alri episodes lasted 15 days or more without giving any more details . median duration of uri and lri episodes has been reported to be 14 days ( range : 725 days ) and 19 days ( range : 939 days ) in the greenland study . incidence of uri was the highest in the 1217-month - age cohort , while that for pneumonia was highest in 0 - 1-month - age cohort . the bangladesh   study found the highest uri incidence among children 1823 months old , followed by infants 611 months old , while the highest pneumonia incidence was reported in infants 06 months old , followed by children 1218 months old . the greenland study   also reported the highest prevalence of respiratory symptoms in the 611 months age group with a steep rise occurring from less than 5 months to 611 months and a decrease in incidence thereafter . thus , the risk of ari generally increases in the later part of life as a toddler , which could be due to the fact that children become more mobile at this age and interact with multiple caregivers and individuals ( in contrast to mother only during early infancy ) and they are therefore exposed to more numbers of ari cases / carriers . 
 gender . our finding of slightly higher incidence of  no pneumonia , cough , and cold  in girls did not match the findings of nfhs which reported slightly higher prevalence among boys . the reasons for higher reporting for boys could be explained by the gender bias that is prevalent in our society with its attendant preferential treatment for boy - child , especially when history is the only method of assessment ( nfhs methodology ) . the greenland study   did not find any gender differential as far as uris were concerned , but that for pneumonia was higher in boys . the presentstudydemonstrated that uri peaks in spring season and to a lesser extent in autumn , while pneumonia peaks a little later . the bangladesh   study noted a higher incidence of uri as well as pneumonia ( alri ) in monsoon and autumn ( before winter ) . on the other hand , no seasonal pattern in the incidence of ari , uri , or lri was observed in the greenland study . the differences are possibly due to differences in the climatic conditions as well as housing conditions of the areas of study . the annual incidence of aris was 4.1 episodes / child , while that for pneumonia was 0.44 episodes / child . pneumonia incidence was higher than the estimates for india as well as for south asia as a whole . incidence of pneumonia was roughly one - tenth that of ari and that of severe pneumonia or otitis media was one - tenth that of pneumonia . since incidence of aris and pneumonia generally decreased with increasing age , targeting infants specifically for prevention and control efforts may be a more effective strategy . two fortnight - long intensive mass - media campaigns ( pneumonia awareness and prevention fortnight ) prior to holi ( a festival of colors celebrated in the month of march commencing the spring season ) and dusshera ( indian festival celebrated in autumn during month of october / november ) , on the lines of  breast feeding awareness week  and  malaria month ,  just before onset of the peak season , are also likely to be helpful in generation awareness and disease control . more of such studies with larger sample sizes and including rural as well as urban populations need to be conducted . ( i ) with the study being conducted in a small area , its findings may not be generalizable to other peri - urban settings , within and outside this country . ( ii ) period of recall of one fortnight , though accepted as standard for this type of study , may have led to missing out on many episodes ( those starting after a particular visit and ending before the next ) , particularly when primary caregiver was not the respondent . ( iii ) primary researcher being a doctor was ethically bound to provide health education as well as medical guidance to children and their caregivers , thereby altering the natural history and may be even the incidence of aris .
acute respiratory infections ( aris ) in spite of being the single most important under - five morbidity have not been studied adequately in peri - urban settings in india . 
 we conducted this study prospectively on a cohort of 106 children in a peri - urban area of delhi . 
 the overall 2-week prevalence of all types of ari was 34.3% . 
 annual combined incidence of all types of ari was 7.9 episodes/100 child - weeks ; while that for no pneumonia , cough , and cold , pneumonia , and otitis media was 7.1 , 0.85 , and 0.09  epi/100  ch - wks , respectively . 
 incidence of ari was higher in infancy ( 9.4  epi/100  ch - wks ) as compared to toddlers ( 7.0  epi/100  ch - wks ) . 
 pneumonia incidence was higher among boys ( 0.9  epi/100  ch - wks as compared to 0.6 for girls ) and the highest in infants under 2 months of age ( 1.09  epi/100  ch - wks ; p < 0.01 ) . 
 incidence of severe pneumonia was roughly one - tenth that of pneumonia . 
 incidence of both ari and pneumonia peaked in spring and autumn . 
 mothers of infants , zespecially those under 2 months of age , need to be made aware of ari / pneumonia and iec campaigns may be aired more intensively keeping their peak season in mind .