MINI-SYMPOSIUM: RESPIRATORY VIRUSES – PART IEpidemiology and seasonality of respiratory tract virus infections in the tropics
Section snippets
INTRODUCTION
Respiratory tract infections (RTI), a large proportion of which are viral, account for the majority of acute illnesses at all ages worldwide.1., 2. They are a significant cause of morbidity and mortality at the extremes of age and in high-risk individuals. In temperate regions of the world, there is a clear seasonal variation in their occurrence, with peaks during the cold winter months. This variation is less apparent in the tropics, where there is less fluctuation in ambient temperature.
SEASONALITY OF RESPIRATORY VIRUSES IN THE TROPICS
One of the earliest studies that suggested a seasonal pattern to respiratory virus infections in the tropics was carried out on an isolated island in the West Indies.5 In that study, the authors examined the incidence of “colds”, which were essentially acute upper respiratory tract infections (URTI). They studied the entire population (about 700 individuals) prospectively over 12 months and found evidence that an increased incidence of URTI was associated with a decrease in environmental
AGE AND SEX DISTRIBUTION OF RTIS IN THE TROPICS
RTIs are common in children, and they decrease with increasing age. This is similar in both temperate and tropical regions. It is clearly reflected in the comprehensive study of inpatients and outpatients with RTI in Taiwan. Of 523 virus-infected children, 32.5% were under the age of 1 year, 37.7% were aged 1–3 years, 17.2% aged 3–6 years, 7.3% aged 6–10 years and only 1.9% were above the age of 10 years.16 In Senegal, 64.1% of patients presenting to seven healthcare units with influenza-like
AETIOLOGY OF RTI IN THE TROPICS
Community-based studies with sampling for viral isolation provide the best information about the aetiology of RTI. Unfortunately, there is a paucity of such studies in the tropics. In the study from North-east Brazil, rhinovirus was found in 45.6% of the virus-positive samples, followed by parainfluenza (16%), enterovirus (15.8%), adenovirus (9.9%) and influenza (5.7%).25 Another study in Thailand32 found RSV, parainfluenza and adenovirus to be the main pathogens in acute RTI. Rhinovirus was
MORTALITY AND MORBIDITY OF RTI IN THE TROPICS
Improvement in healthcare and implementation of vaccination policies have somewhat lessened the scourge of infectious disease in many countries. Regarding viral RTI, it is difficult to assess mortality because of the lack of community-based studies, use of less-sensitive viral-isolation techniques and the presence of superimposed bacterial infection. For RSV infection, mortality in developed countries is estimated to be between 0.3 and 1%.36., 37. It is similarly low in Hong Kong (0.15%)10 and
CONCLUSION
Epidemiological differences exist for RTIs between tropical and temperate regions. There is an obvious seasonal pattern to RSV and influenza infections. The burden of these infections and the advent of new and often expensive treatments such as monoclonal antibodies make it imperative for healthcare providers everywhere to study the impact of respiratory viruses in their country and implement optimal preventive and treatment strategies.
References (38)
- et al.
Epidemiologic patterns of acute lower respiratory disease of children in a pediatric group practice
J. Pediatr.
(1971) - et al.
Improved outcome of respiratory syncytial virus infection in a high-risk hospitalized population of Canadian children. Pediatric Investigators Collaborative Network on Infections in Canada
J. Pediatr.
(1992) - et al.
Current estimates from the National Health Interview Survey, 1995
Vital Health Stat.
(1998) - et al.
Respiratory syncytial virus infection in tropical and developing countries
Trop. Med. Int. Health
(1998) - et al.
1993 morbidity survey of outpatients
Singapore Fam. Phys.
(1994) - Maimunah AH, Pathmanathan I. The Underfives: Acute Respiratory Illnesses. National Health and Morbidity Survey Report....
- et al.
A bacteriological study of “colds” on an isolated tropical island (St John, United States Virgin Islands, West Indies)
J. Exp. Med.
(1931) Epidemiology of acute respiratory infections in children of developing countries
Rev. Infect. Dis.
(1991)Epidemiology of viral respiratory infections
Am. J. Med.
(2002)- et al.
Seasonal trends of viral respiratory tract infections in the tropics
Epidemiol. Infect.
(1998)