Respiratory virus infections are one of the major causes of hospitalizations, and outbreaks of respiratory virus infection have led to severe economic loss. In addition to pulmonary complications, respiratory viruses can also lead to non-pulmonary complications.

However, many previous studies on the complications of respiratory viruses are retrospective in nature, and therefore many patients with respiratory virus infection may not be tested. Furthermore, these studies did not take into account that respiratory viruses can be found in some asymptomatic individuals. The aim of this study is to capture the burden of respiratory viruses in patients with acute pulmonary and extrapulmonary complications. We will recruit patients admitted to our hospital with acute coronary syndrome, stroke and exacerbation of underlying lung diseases. We will collect saliva from these patients and test for respiratory viruses. As controls, we will recruit asymptomatic patients at the out-patient clinic for follow up of chronic heart, lung or neurological diseases.

We anticipate that this study will greatly enhance our understanding of the epidemiology of respiratory viruses in acutely hospitalized patients. Our findings will be important for clinicians, public health practitioners and scientists.

Respiratory viruses cause severe infections, and contribute to a substantial number of hospitalizations, admission to intensive care units and deaths. Many hospitalizations due to respiratory virus infection are related to pneumonia or exacerbation of chronic lung disease. In addition, many hospitalizations are related to extrapulmonary complications, such as acute coronary syndrome or stroke.

Previous studies have reported the incidence of respiratory viruses among patients with pulmonary complications, or the association of respiratory viruses with acute coronary syndrome or stroke. However, there are several problems associated with these studies. First, many of these studies are retrospective in nature, and therefore testing was only performed in selected patients with respiratory symptoms. Hence, many patients without respiratory symptoms were not recruited. Second, respiratory virus can be detected in some asymptomatic individuals. Therefore, the presence of respiratory virus may be an incidental finding rather than the cause of the complication. Third, many studies only focus on a few respiratory viruses, especially on influenza virus.

This study aims to address these issues. The investigators propose to conduct a prospective cohort study. The investigators will recruit hospitalized adult patients with exacerbation of underlying lung disease, acute coronary syndrome or stroke. As controls, the investigators will recruit outpatients follow-up for chronic heart disease, chronic lung disease or neurological conditions. The investigators will collect saliva from study participants and perform respiratory virus testing using a multiplex PCR panel. Previous studies have shown that there is a high concordance between results from respiratory virus testing on saliva and nasopharyngeal specimens. The investigators will also use a standardized questionnaire to collect information regarding symptoms.

This study will provide accurate data on the epidemiology of respiratory viruses in pulmonary and extrapulmonary complications.These data are important for clinicians, public health practitioners and scientists.

Inclusion Criteria: (For hospitalized patients)

1. Admitted to the acute medical ward of Queen Mary Hospital via the accident and emergency department
2. Aged 18 years or above
3. Hospitalized for less than 24 hours at the time of recruitment
4. Presented with exacerbation of underlying lung disease, acute coronary syndrome or stroke
5. Competent and agree to provide written informed consent

Exclusion Criteria: (For hospitalized patients)

1. Admitted to any hospitals in the past 14 days
2. Respiratory virus testing performed in the past 14 days
3. Antiviral against respiratory virus given within the past 14 days
4. Not sufficient saliva

Inclusion Criteria: (For out-patients)

1. Aged 18 years or above
2. Follow-up at out-patient clinic or at the physiotherapy department of Queen Mary Hospital
3. Competent and agree to provide written informed consent

Exclusion criteria: (For out-patients)

1. Admitted to any hospitals in the past 14 days
2. Respiratory virus testing performed in the past 14 days
3. Antiviral against respiratory virus given within the past 14 days
4. Onset of new respiratory or non-respiratory symptoms within the past 14 days
5. Not sufficient saliva

1. Hospitalized patients with acute coronary syndrome, stroke or exacerbation of underlying lung disease
2. Outpatients follow-up for chronic conditions