Background: Respiratory syncytial virus (RSV) is the most common cause of childhood illness which attack the lower respiratory tract and develop bronchitis and pneumonia. Approximately 70% of infants are infected with RSV during their first year of life, and almost all children are infected at least once by 2 years of age (Wu \& Hartert, 2011).
Each year, an estimated 33·1 million episodes of RSV-associated acute lower respiratory infections occur among under-five children globally, leading to 3·2 million hospitalizations and 118,200 deaths (Ting Shi \& Acacio, 2017). The burden of RSV-associated severe acute lower respiratory tract infection is 10 times higher in developing countries compared to that in developed countries (36.1 per 1000 life birth vs 3.2 per 1000 life birth, respectively).
In addition to acute mortality and morbidity, RSV infection has a long-term effect on children's health (Jat \& Kabra, 2017; Kneyber, Steyerberg, de Groot, \& Moll, 2000). RSV infection can induce a state of bronchial hyper-reactivity that has an association with the development of asthma in later life (Balfour-Lynn, 1996), which, in turn, is a major risk factor of chronic obstructive pulmonary disease in adulthood (Svanes et al., 2010).. The prevalence of wheezing and asthma were reported two times higher in the children who had RSV bronchitis in infancy compared with children without a history of bronchiolitis during infancy (Sigurs et al., 2010). In a report, it was shown that among the children who experienced asthma by school age, 31% of them had healthcare visits in infancy due to respiratory diseases (Wu \& Hartert, 2011). The severity of the RSV associated illness was reported as an additive factor for asthma risk. Hartert et, al., reported that asthma prevalence was two times higher in the infants who were hospitalized for RSV infection compared to the other who received care at the outdoor department (Wu \& Hartert, 2011). In the mouse model, it was found that viral infection in neonatal rats delayed the growth of secondary septa, decreased the alveolar surface density by 14 to 26%, and reduced the diameter of terminal bronchioles by 11 and 20% (Castleman, Sorkness, Lemanske, Grasee, \& Suyemoto, 1988). However, there is no data on the effect of RSV infection on the lung of neonates. In human, the lung remains premature at birth and continue to develop for 2-3 years postnatally and can be assumed that the impact of RSV infection during early infancy would be very severe.
Collecting clinical samples from young infants and lack of appropriate diagnostic to detect RSV virus are the major obstacles to study RSV infection in developing countries. No study from developing countries has investigated the long-term effect of RSV infections incurred during the young infant period. It is assumed that the long-term effect of RSV infection might be more intense if infection occurs during this period, as the lungs of newborns continue to develop for the first several months of life.
Recently, a study aimed to determine the etiology of young infant infection at five centers of three South Asian countries (Bangladesh, India, and Pakistan). This study identified 474 young infants who had laboratory-confirmed RSV infection; additionally, this study tested specimens from 1,873 age and sex-matched healthy infants, which were found to be negative for RSV. The current age of that cohort is between 5 and 7 years, which provides a unique opportunity to gather information on the long-term effect of RSV infection in a large number of laboratory-confirmed cases at a low cost.
Given the relative frequency and impact of RSV infection in developing healthcare settings, should the investigators identify a high prevalence of subsequent wheeze and asthma the potential benefit of interventions to reduce RSV will be enhanced. In addition, this study will have the following supplementary benefits (1) the ability to report the feasibility to identify wheeze frequency by self-reporting in South Asian populations, (2) the feasibility and outcomes of tests that are utilized to support the diagnosis of asthma and other respiratory diseases in children, i.e. skin prick tests, Eosinophil count and spirometry.
Research Questions: The overarching aim of this study is to understand the long-term effect on child health of RSV infection occurring in the first two months of life. Therefore, through this study, the investigators aim to investigate the following research questions:
1. Is there an association between RSV infection in the first two months of life and development of asthma later in childhood?
2. Is the lung function of children who had RSV infection in the first 2 months of life lower than that of children who did not have RSV infection?
3. Is there an association between RSV infection in the first two months of life and physical development in childhood?
4. Are risk factors for childhood asthma different for the children who had RSV infection in the first two months of life than others without RSV infection at the same age?
Methodologies: The investigators have identified sites of the Aetiology of Neonatal Sepsis in South Asia (ANISA) study, two in Pakistan and one each in Bangladesh and India to implement this study. Health workers will visit the households of eligible children. Children whose parents provide consent will be visited three times in one year period, at baseline, after six months and the end of the year. In the first visit, a member of the research team will explain the study objectives and procedures to one of the family members (primarily the mother) of the eligible children to provide consent for enrolling the children in the study, the parents of the enrolled children will be interviewed using a structured questionnaire to record the current and previous health status of children. Study team members will remain blind about the RSV infectious status of the children to avoid enrollment bias. To ascertain asthma and wheeze, parents will be inquired about breathing difficulties of the children using a questionnaire designed by the International Study of Allergies and Asthma in Childhood (ISAAC), dermatitis will be defined by the criteria provided by The U.K. Working Party's Diagnostic Criteria for Atopic Dermatitis. It was previously reported that terms such as ''wheeze'' and ''difficulty in breathing'' used in the ISAAC questionnaire have little validity when comparing clinical cases between parents and also between clinicians, and the conceptual understandings of ''wheeze'' for parents of children with reported wheeze are different from definitions used in epidemiology (Bisgaard \& Szefler, 2007). To reduce the differences in patient responses, the research team will provide a video demonstration of wheeze and asthma-like symptoms to the parents before introducing the questionnaire. They will also introduce a child "case card" to the parents and request to record the wheezing episodes of their enrolled children using this case card. Additionally, they will also request the parents to reach team (over the phone) if they notice wheezing sound to their children, a research team will visit the symptomatic children and perform a physical assessment of the child using auscultation and peak flowmetry. The research team will return to the families after six months to emphasize the use of the case card for recording wheeze episodes and also refer the children to the health facilities for physical assessment (spirometry, exercise challenge test, skin prick test, and eosinophil count test and anthropometric measurements). In the health facilities, physicians will perform afore mention tests and procedures. The research team will return to the families again after one year of the first visit and collect the "case card" from where they will record the number of wheeze/asthma episode occurred in the last one year (follow-up period).
