INTRODUCTION
Influenza and respiratory syncytial virus (RSV) are respiratory
pathogens that cause a substantial disease burden among adults aged 65
years and above [1]. Global estimates suggest that around two-thirds
of all seasonal influenza-related mortality occurs among older adults
with more than 260,000 deaths annually [2]. Data from developed
countries show that respiratory illnesses due to RSV among older adults
may exceed one million episodes and cause around 14,000 in-hospital
deaths every year [3]. Older adults with cardiopulmonary conditions
are at increased risk for severe illness due to influenza and RSV
infection [4, 5]. However, it is not fully established whether
cardiopulmonary conditions present an increased risk for influenza and
RSV infections, and there are little data on the burden of infection
from these pathogens among persons with cardiopulmonary conditions in
middle-income countries.
Thailand is an upper-middle-income country in tropical Southeast Asia,
where recognition of influenza and RSV disease burden is growing. Since
2008, adults aged ≥65 years and those with chronic diseases have been
recommended for annual influenza vaccination by the Thai Ministry of
Public Health (MoPH) [6]. Nonetheless, influenza vaccine uptake
among older adults is still less than 20% (Bureau of General
Communicable Diseases, Thailand MoPH). Studies among hospitalized
patients suggest that the prevalence of RSV-associated respiratory
illnesses in Thailand is around 2-9% among older adults [7-11].
However, reliable estimates of the infection rates in the community
remain limited. Using data from a longitudinal prospective cohort study
of influenza vaccine effectiveness among rural community-dwelling Thai
adults aged ≥65 years [12], we compared the incidence of influenza
and RSV in those with and without cardiopulmonary conditions.