This household-based prospective cohort study aims to stablish the household transmission of Respiratory syncytial virus and S. pneumoniae especially in the elderly and infants/children as well as inter-relationship between S. pneumoniae and Respiratory syncytial virus.

A household-based prospective cohort study will be conducted from 2021 to 2025 in northern Taiwan. We will invite 240 households, having a baby who is discharged from MacKay children's Hospital. The households will be classified into nuclear family type and extended family type. The "Nuclear family type" is defined as husband and wife with baby (aged less than 5 months) and with or without children (2-5) and the "Extended family type" (three-generation family) is defined as husband and wife with baby (aged less than 5 months), children (2-5), and grandparents aged > 65 years old. We will initially complete an enrollment form to collect baseline data, including patient demographics, prior medical history, season when discharge, neonatal course and households. A LINE-based management will be done weekly by study team to see if there are any respiratory symptoms in household. In addition to the monthly physician weekly LINE response, the research nurse will contact the parents or legal guardians by telephone monthly for the 24 months to obtain data on changes in baseline information, and specific facts regarding possible respiratory infections after the last contact. If the households present with respiratory symptoms, the visit will be arranged as early as possible. When they presenting to the emergency department, outpatient clinic, or inpatient ward, the urine will be collected for the serotype-specific urinary antigen detection (SSUAD) assays and the nasopharyngeal or throat swab for polymerase chain reaction will be performed to study serotype of S. pneumoniae and Respiratory syncytial virus subgroup. If the subjects who have clinical syndromes suggestive of pneumonia or bronchopneumonia, they will be asked to participate in the further study along with their household family members. Nasopharyngeal aspiration, urine, blood, and induced sputum will be collected for cultures, polymerase chain reaction and serological test. Clinical manifestations, disease course, and outcomes will be recorded. Family members in the same household will asked to undergo screening with a nasopharyngeal or throat swab and urine sample. We will trace back 2-week contact history of children in nuclear family who get Respiratory syncytial virus or pneumococcal infections, especially focus on other family members. The data will be further analyzed to evaluate the influence of short period and long period contact.

Inclusion Criteria:

• Indicator case: Babies under 5 months of age were born in Mackay Children's Hospital and had no acute respiratory infection-like symptoms that required medical intervention when they agreed to participate in the trial.
• Family members: family members living with the Indicator case, including 2-5 years old siblings, parents and grandparents over 65 years old.
• Willing to sign the informed consent form and agree to join the official LINE account to receive research tracking.

Exclusion Criteria:

• Babies older than 5 months
• Co-morbid medical conditions of the baby such as chronic lung disease, cyanotic congenital heart disease, neuromuscular disease and a primary immunodeficiency.
• Family members who do not live with the Indicator case
• Family with grandparents younger than 65 years old
• Someone living with family members refuses to participate in the research.
• Unwilling to sign informed consent form or refuse to join the official LINE account to receive tracking.

A household-based prospective cohort study will invite 240 households, having a baby who is discharged from MacKay children's Hospital. The households will be classified into nuclear family type and extended family type. The "Nuclear family type" is defined as husband and wife with baby (aged less than 5 months) and with or without children (2-5) and the "Extended family type" (three-generation family) is defined as husband and wife with baby (aged less than 5 months), children (2-5), and grandparents aged > 65 years old.

We will record and analyze the individual participant data by our study team only.