The respiratory viruses are recognized as the most frequent lower respiratory tract pathogens for infants and young children in developed countries but less is known for developing populations. The authors conducted a prospective study to evaluate the occurrence, clinical patterns, and seasonal trends of viral infections among hospitalized children with lower respiratory tract disease (Group A). The presence of respiratory viruses in children's nasopharyngeal was assessed at admission in a pediatric ward. Cell cultures and immunofluorescence assays were used for viral identification. Complementary tests included blood and pleural cultures conducted for bacterial investigation. Clinical data and radiological exams were recorded at admission and throughout the hospitalization period. To better evaluate the results, a non- respiratory group of patients (Group B) was also constituted for comparison. Starting in February 1995, during a period of 18 months, 414 children were included- 239 in Group A and 175 in Group B. In Group A, 111 children (46.4%) had 114 viruses detected while only 5 children (2.9%) presented viruses in Group B. Respiratory Syncytial Virus was detected in 100 children from Group A (41.8%), Adenovirus in 11 (4.6%), Influenza A virus in 2 (0.8%), and Parainfluenza virus in one child (0.4%). In Group A, aerobic bacteria were found in 14 cases (5.8%). Respiratory Syncytial Virus was associated to other viruses and/or bacteria in six cases. There were two seasonal trends for Respiratory Syncytial Virus cases, which peaked in May and June. All children affected by the virus were younger than 3 years of age, mostly less than one year old. Episodic diffuse bronchial commitment and/or focal alveolar condensation were the clinical patterns more often associated to Respiratory Syncytial Virus cases. All children from Group A survived. In conclusion, it was observed that Respiratory Syncytial Virus was the most frequent pathogen found in hospitalized children admitted for severe respiratory diseases. Affected children were predominantly infants and boys presenting bronchiolitis and focal pneumonias. Similarly to what occurs in other subtropical regions, the virus outbreaks peak in the fall and their occurrence extends to the winter, which parallels an increase in hospital admissions due to respiratory diseases.
Croup is a common manifestation of respiratory tract infection in children, and human parainfluenza virus 1 (HPIV-1) is the agent most commonly associated with croup. In the United States, HPIV-1 produces a distinctive pattern of biennial epidemics of respiratory illness during the autumn months of odd-numbered years. National Hospital Discharge Survey data for croup hospitalizations among patients <15 years old between 1979 and 1993 were examined along with laboratory-based surveillance data on HPIV-1 activity in the United States. The mean annual number of croup hospitalizations was 41,000 (range, 27,000-62,000/year). Ninety-one percent of hospitalizations occurred among children <5 years of age. Minor peaks in croup hospitalizations occurred each year in February, and major peaks occurred in October of odd-numbered years, coincident with peak HPIV-1 activity. Each biennial epidemic of HPIV-1 was associated with 18,000 excess croup hospitalizations nationwide.
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