Antigenic characterization of respiratory syncytial virus associated with acute respiratory infections in Uruguayan children from 1985 to 1987

Respiratory syncytial virus infection among adults after hematopoietic stem cell transplantation

Introduction:

Respiratory syncytial virus (RSV) is a common cause of morbidity among hematopoietic stem cell transplant (HSCT) recipients, with RSV-associated lower respiratory tract infection carrying high mortality rates. There have been no large studies till date, describing the incidence, clinical features, and outcomes of RSV infection among adult HSCT recipients in India.

Methods:

A prospective cohort of 100 adults who underwent HSCT was followed up for a maximum period of 18 months starting from the date of transplantation for any episode of respiratory tract infectious disease (RTID). Respiratory samples were collected for laboratory confirmation of the presence and subtyping of RSV by real-time reverse transcriptase-polymerase chain reaction.

Results:

The study population comprised of 66% (66/100) males and 34% (34/100) females. Autologous HSCT recipients constituted 78% (78/100) and allogeneic HSCT recipients constituted 22% (22/100) of the study population. The incidence of RSV-RTID among adults after HSCT was 0.82/100 patient months. Most cases occurred during the winter season and the predominant subtype was RSV-A (9/11, 81.8%). Lower RTID was the most common clinical diagnosis made at presentation (9/11, 81.8%). Female gender was predictive of RSV-RTID (log rank P = 0.002). All the RSV-RTID episodes recovered completely without targeted therapy.

Conclusion:

RSV is a significant cause of morbidity among adult HSCT recipients in India. Prophylaxis and treatment measures need to be instituted after a proper risk-benefit assessment. Longitudinal studies with larger sample sizes are needed to confirm these results.

Detection of 12 respiratory viruses with two-set multiplex reverse transcriptase-PCR assay using a dual priming oligonucleotide system

BACKGROUND

We intended to evaluate the diagnostic usefulness of a multiplex reverse transcriptase- PCR (mRT-PCR) assay kit under dual priming oligonucleotide system (DPO) for the childhood acute respiratory tract infections.

METHODS

Two hundred nasopharyngeal aspirates were taken from children < or =5 yr old admitted due to acute respiratory infections in 2004. Direct fluorescent antibody (FA) assays were performed with fresh specimens; then, mRT-PCRs for the detection of 12 respiratory viruses (Seeplex RV detection kit, SeeGene, Seoul, Korea) were tested with frozen specimens.

RESULTS

FA assays for five common respiratory viruses showed positive results in 66 patients (33.0%), while mRT-PCR detected causative viruses in 112 patients (56.0%), including 16 co-infected cases (8.0%). A total of 129 viruses were identified: respiratory syncytial virus A/B (38.0%/7.8%), influenza virus A/B (10.1%/5.4%), parainfluenza virus 1/2/3 (7.0%/3.1%/7.8%), coronavirus 229E or NL63 (6.2%), human metapneumovirus (4.7%), adenovirus (4.7%), rhinovirus (3.9%), and coronavirus OC43 (1.6%).

CONCLUSIONS

DPO-based mRT-PCR was found as a sensitive tool for the detection of the viruses that cause childhood respiratory infections. Clinical significances of the agents detected by mRTPCR need further evaluations.

Climatic, temporal, and geographic characteristics of respiratory syncytial virus disease in a tropical island population

Respiratory syncytial virus (RSV) is an important cause of morbidity in children worldwide, although data from equatorial regions are limited. We analysed climatic, spatial, and temporal data for children presenting to hospitals in Lombok island, Indonesia with clinical pneumonia. During the study period, 2878 children presented and 741 RSV cases were identified. In multivariate analysis with an 8-day lag, occurrence of rain was associated with 64% higher incidence of RSV disease [incidence rate ratio (IRR) 1.64, 95% confidence interval (CI) 1.13-2.38]. A 1% rise in mean relative humidity and 1 degree C increase in mean air temperature was associated with a 6% (IRR 1.06, 95% CI 1.03-1.10) and 44% (IRR 1.44, 95% CI 1.24-1.66) increase in RSV cases, respectively. Four statistically significant local clusters of RSV pneumonia were identified within the annual island-wide epidemics. This study demonstrates statistical association of monsoon-associated weather in equatorial Indonesia with RSV. Moreover, within the island-wide epidemics, localized RSV outbreaks suggest local factors influence RSV disease.

Molecular epidemiology of human respiratory syncytial virus in Uruguay: 1985-2001--a review

The variability of the G glycoprotein from human respiratory syncytial viruses (HRSV) (groups A and B) isolated during 17 consecutive epidemics in Montevideo, Uruguay have been analyzed. Several annual epidemics were studied, where strains from groups A and B circulated together throughout the epidemics with predominance of one of them. Usually, group A predominates, but in some epidemics group B is more frequently detected. To analyse the antigenic diversity of the strains, extracts of cells infected with different viruses of group A were tested with a panel of anti-G monoclonal antibodies (MAbs). The genetic variability of both groups was analyzed by sequencing the C-terminal third of the G protein gene. The sequences obtained together with previously published sequences were used to perform phylogenetic analyses. The data from Uruguayan isolates, together with those from the rest of the world provide information regarding worldwide strain circulation. Phylogenetic analyses of HRSV from groups A and B show a model of evolution analogous to the one proposed for influenza B viruses providing information that would be beneficial for future immunization programs and to design safe vaccines.

Respiratory syncytial virus infections during an epidemic period in Salvador, Brazil. Viral antigenic group analysis and description of clinical and epidemiological aspects

Acute respiratory infections (ARI) caused by respiratory syncytial virus (RSV) were studied in 482 children from Salvador, BA, Brazil, over a period of 12 months. The epidemic period of RSV infections in Salvador occurred from February (summer) to August (winter), with peaks in May, June, and July. The grouping characteristics of 84 RSV present in nasopharyngeal secretions of children seen at a reference university hospital were analyzed. RSV represented 17.4% of all cases and 54.5% of the positive samples. Sixty-four RSV strains were assigned to group A and 14 to group B. Both groups circulated in the five months of the epidemic period studied. Infections by both groups of RSV were more frequent in children up to one year of age. The incidence of RSV ARI was slightly more frequent in males, although group B had more infected females.

Respiratory syncytial virus epidemics: the ups and downs of a seasonal virus

Respiratory syncytial virus (RSV) is the most common pathogen causing lower respiratory tract infections in infants worldwide. Lower respiratory tract infections caused by RSV occur epidemically, and the appearance of epidemics seems to vary with latitude, altitude and climate. This study uses a review of the literature on RSV seasonality to investigate whether a global pattern in RSV epidemics can be found. A comparison of morbidity and mortality caused by RSV in developed vs. developing countries is also presented. The seasons in which RSV epidemics occur typically depend on geographic location and altitude. During these seasons the epidemics tend to appear in clusters. Although the appearance pattern of these epidemics varies from one continent to another, they usually begin in coastal areas. RSV is the cause of one-fifth of lower respiratory infections worldwide. Generally RSV mortality is low, with a median value of zero. However, RSV mortality in developing countries is significantly higher than RSV mortality in developed countries.

Viral etiology of acute respiratory infections among children in Porto Alegre, RS, Brazil

Although acute respiratory infections (ARIs) are a major cause of child morbidity and mortality in Southern Brazil, little information is available on their seasonality and viral etiology. This study was conducted on children under 5 years of age with ARI to assess viral etiology in the State of Rio Grande do Sul, from 1990 to 1992. A total of 862 nasopharyngeal secretion (NPS) samples were tested using indirect immunofluorescence. The results showed that 316 (36.6%) NPS samples were positive: 26.2% for RSV, 6% for adenovirus, 1.7% for influenza viruses, 1.5% for parainfluenza viruses, and 1.2% for mixed infection. The mean viral prevalence rates in out-patient services, emergency wards, and in-patient hospital wards were 26.7%, 53% and 42.3%, respectively. Respiratory syncytial virus (RSV) and adenovirus accounted for 91.4 % of the viral diagnoses. RSV was more frequent in children under one year of age at the three levels of health care and was prevalent in infants under six months. Adenovirus was the most prevalent pathogen in hospitalized children, in 1992. Influenza A virus showed an increased prevalence with age among out-patient children. This study shows the annual occurrence of viral respiratory infections in the coldest months, with a significant annual variation in the frequency of RSV infection.

Clinical patterns and seasonal trends in respiratory syncytial virus hospitalizations in São Paulo, Brazil

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.

Respiratory syncytial virus groups A and B in Porto Alegre, Brazil, from 1990 to 1995 and 1998

We analyzed the respiratory syncytial virus (RSV) groups and their epidemiological pattern that were detected over the course of seven years in southern Brazil. The two RSV groups co-circulated each year, but frequencies of groups A and B varied both between and within yearly outbreaks. In 1991, group A predominated over group B (p=0.0016). RSV outbreaks analyzed showed a temperature-dependent pattern and no association with rainfall, similarly to other countries from southern South America. Knowledge of the variants is important in terms of both diagnosis and definition of a vaccine composition.

Clinical and epidemiologic characteristics of respiratory syncytial virus subgroups A and B infections in Santa Fe, Argentina

Respiratory Syncytial Virus (RSV) has two major antigenic groups, A and B. The implications of these variants in the epidemiology and pathogenesis of RSV infection are not well defined. This study was undertaken to compare the two RSV subgroups in patients admitted to hospital. Clinical and epidemiologic features of RSV subgroups in children under 30 months of age with proven RSV acute lower respiratory infections were examined during 4 winters from 1993 to 1996 in Santa Fe, Argentina. RSV typing was carried out with monoclonal antibodies in nasopharyngeal cells by indirect immunofluorescence. Of the 177 RSV positive nasopharyngeal aspirates obtained from 1993 to 1996, 85 (48%) were available for typing. Seventy-three (85.9%) specimens were identified as Subgroup A and 12 (14.1%) as Subgroup B. Except in 1993, in which only Subgroup A was detected, both variants circulated throughout the epidemic season. Subgroup A infections produced more severe disease than Subgroup B infections, as assessed by the length of the hospital stay and the use of respiratory support. This difference was age related, being evident in infants 0-6 months old. Patients with Subgroup B infections were also significantly less frequently breast-fed (95% vs. 75% for A and B subgroups, respectively; P = 0.04). It is concluded that the severity of disease in Argentinian patients admitted with acute RSV infections may be associated with Subgroup A strains as determined by a serogrouping method.

Respiratory syncytial virus genetic and antigenic diversity

Respiratory syncytial virus (RSV) is a major cause of viral lower respiratory tract infections among infants and young children in both developing and developed countries. There are two major antigenic groups of RSV, A and B, and additional antigenic variability occurs within the groups. The most extensive antigenic and genetic diversity is found in the attachment glycoprotein, G. During individual epidemic periods, viruses of both antigenic groups may cocirculate or viruses of one group may predominate. When there are consecutive annual epidemics in which the same group predominates, the dominant viruses are genetically different from year to year. The antigenic differences that occur among these viruses may contribute to the ability of RSV to establish reinfections throughout life. The differences between the two groups have led to vaccine development strategies that should provide protection against both antigenic groups. The ability to discern intergroup and intragroup differences has increased the power of epidemiologic investigations of RSV. Future studies should expand our understanding of the molecular evolution of RSV and continue to contribute to the process of vaccine development.

Respiratory syncytial virus genetic and antigenic diversity

Respiratory syncytial virus (RSV) is a major cause of viral lower respiratory tract infections among infants and young children in both developing and developed countries. There are two major antigenic groups of RSV, A and B, and additional antigenic variability occurs within the groups. The most extensive antigenic and genetic diversity is found in the attachment glycoprotein, G. During individual epidemic periods, viruses of both antigenic groups may cocirculate or viruses of one group may predominate. When there are consecutive annual epidemics in which the same group predominates, the dominant viruses are genetically different from year to year. The antigenic differences that occur among these viruses may contribute to the ability of RSV to establish reinfections throughout life. The differences between the two groups have led to vaccine development strategies that should provide protection against both antigenic groups. The ability to discern intergroup and intragroup differences has increased the power of epidemiologic investigations of RSV. Future studies should expand our understanding of the molecular evolution of RSV and continue to contribute to the process of vaccine development.

Respiratory syncytial virus infection in tropical and developing countries

Little is known about the epidemiology of respiratory syncytial virus (RSV) infection in tropical and developing countries; the data currently available have been reviewed. In most studies, RSV was found to be the predominant viral cause of acute lower respiratory tract infections (ALRI) in childhood, being responsible for 27-96% of hospitalised cases (mean 65%) in which a virus was found. RSV infection is seasonal in most countries; outbreaks occur most frequently in the cold season in areas with temperate and Mediterranean climates and in the wet season in tropical countries with seasonal rainfall. The situation on islands and in areas of the inner tropics with perennial high rainfall is less clear-cut. The age group mainly affected by RSV in developing countries is children under 6 months of age (mean 39% of hospital patients with RSV). RSV-ALRI is slightly more common in boys than in girls. Very little information is available about the mortality of children infected with RSV, the frequency of bacterial co-infection, or the incidence of further wheezing after RSV. Further studies on RSV should address these questions in more detail. RSV is an important pathogen ill young children in tropical and developing countries and a frequent cause of hospital admission. Prevention of RSV infection by vaccination would have a significant impact on the incidence of ALRI in children in developing countries.

Etiology and severity of community acquired pneumonia in children from Uruguay: a 4-year study

The 4-year study (1987-1990) covered the major clinical-epidemiological characteristics of pneumonia in children as diagnosed at the emergency service of the Children's Hospital, as well as etiologies, and factors involved in the most severe cases. Etiology was determined in 47.7% of the 541 pneumonia cases, involving 283 pathogens of which 38.6% were viruses and 12.6% bacteria. Viral and mixed etiologies were more frequent in children under 12 months of age. Bacteria predominated in ages between 6 and 23 months. Among the viruses, respiratory syncytial virus predominated (66%). The bacterial pneumonias accounted for 12.2% of the recognized etiologies. The most important bacterial agents were S. pneumoniae (64%) and H. influenzae (19%). H. influenzae and mixed infections had a relevant participation during the 1988 season, pointing to annual variations in the relative participation of pathogens and its possible implication in severity of diseases. Correlation of severity and increased percentage of etiological diagnosis was assessed: patients with respiratory rates over 70 rpm, or pleural effusion and/or extensive pulmonary parenchyma compromise yielded higher positive laboratory results. Various individual and family risk factors were recognized when comparing pneumonia children with healthy controls.

Subgrouping of respiratory syncytial virus strains from Australia and Papua New Guinea by biological and antigenic characteristics

Strains of respiratory syncytial virus from 3 major areas of Australia and Papua New Guinea (PNG) were analyzed for variations in their antigenic and biological properties and in the molecular weights of their major structural proteins. Seventy-eight strains from infants and young children with LRI were collected from 1981-1984. The RSV season in the Australian cities lasted from April through September, with major peaks in July of each year, while the RSV season in tropical PNG was year-round, with small peaks in March and October of each year coinciding with excessive rainfall. Fifty-six strains were analyzed in detail; 40 were typed by time-resolved fluoroimmunoassay with monoclonal antibodies as group A strains and 16 were group B; both groups were concurrent. Three children of one family had sequential RSV infections 13 months apart, and the etiologic group A strain was identical both years in terms of growth and antigenic properties with strain-specific ferret antisera; the second infection was milder in all three children. On average, the group A strains replicated considerably better than group B strains in HEp2 cells, producing 53% more syncytia and 99% higher infectious virus titers in 31% less time in culture. Ten group A and B reference strains exhibited the same growth patterns as the A and B regional strains, respectively. Differences in antigenicity as measured with hyperimmune antisera to prototype Long strain were even greater. Group A strains exhibited a mean 68% greater IFA staining than B strains, a 71% greater EIA reaction, and were neutralized to 69% higher serum titers than B strains. Again, the reference A and B strains included as controls gave patterns identical to those of the regional strains. Finally, the P phosphoprotein had consistently higher molecular weight in A strains (mean 35,900) than B strains (mean 33,100). Small variations in the sizes of the F and G glycoproteins were not sufficient to suggest grouping on this basis.

Respiratory syncytial virus subgroup B dominance during one winter season between 1987 and 1992 in Vancouver, Canada

A subgroup analysis of 613 specimens submitted to the British Columbia's Children's Hospital from 1987 to 1992 revealed that subgroups A and B of respiratory syncytial virus (RSV) were both circulating in our community, with some predominance for subgroup A during the period from October 1987 to September 1988 (the 1987-88 season) (64%), 1990-91 (60%), and 1991-92 (62%). During 1989-90 subgroup A represented the majority of isolates (80%). Subgroup B predominated during only one season, 1988-89 (94%). No microheterogeneity within subgroups was apparent as judged by the monoclonal antibody reactivity pattern. More male than female children were affected overall, but no sex-related difference between subgroup infections could be detected (P = 0.28). The majority of patients were less than 1 year of age, and no significant association between age and subgroup was detected after stratifying for year (P = 0.64). This is, to our knowledge, the first comprehensive longitudinal RSV subgroup prevalence study from the Pacific Northwest and from Canada.

Respiratory syncytial virus (RSV) bronchiolitis: comparative study of RSV groups A and B infected children

The grouping characteristics of 29 respiratory syncytial virus (RSV) present in nasopharyngeal cells collected from hospitalized children with bronchiolitis during the 1990 RSV season in Porto Alegre, RS, were analysed. Twenty-two were grouped as belonging to group A and 7 to group B. Cyanosis, oxygen therapy, cough, length of hospitalization and atelectasis were observed to be more frequently found within group B infected children. Other clinical signs and symptoms were similarly found in both groups.

Antigenic diversity of respiratory syncytial viruses and its implication for immunoprophylaxis in ruminants

Bovine respiratory syncytial virus (BRSV) is a very important pathogen of cattle and perhaps other ruminants. It is a major contributor to the incidence of respiratory tract disease in nursing beef and feedlot and dairy calves. The genome of respiratory syncytial viruses encodes 10 proteins translated from 10 unique mRNAs. The major glycoprotein (G), fusion protein (F), 1A protein and the 22K protein are components of the viral envelope. The nucleocapsid contains the nucleocapsid protein (N), the phosphoprotein (P), and the large protein (L). The matrix protein (M) forms a structural layer between the envelope and the nucleocapsid. Antibodies to all the structural proteins develop in convalescent calves. However, evidence suggests that immunity develops primarily as a result of the antigenic stimulus by the major glycoprotein G and the fusion glycoprotein F. It is known also that activated cytotoxic T cells interact with N and F protein antigens and helper T cells interact with N, F, and 1A protein antigens. With the exception of the major glycoprotein, the respective proteins of various respiratory syncytial viruses share major antigenic domains. Based on antigenic differences of the major glycoprotein, at least 3 subgroups of RSV are recognized; human A, human B, and bovine RSV. Indirect evidence suggests that a second subgroup of BRSV exists. However, we have identified only one BRSV subgroup based on our work with RNase mismatch cleavage analysis of the G protein gene from a limited number of strains. Furthermore, our data indicated that a caprine RSV isolate is closely related to the bovine strains, but an ovine isolate is not. The latter may constitute yet another subgroup of RSV. These data affect decisions on optimization of immunoprophylaxis since evidence suggests that protection against a homologous RSV subgroup virus is superior to that against a heterologous strain in immune subjects.

Evolution of the G and P genes of human respiratory syncytial virus (subgroup A) studied by the RNase A mismatch cleavage method

The G and P genes of human respiratory syncytial viruses (subgroup A), isolated between 1961 and 1989, were analyzed by RNase A one-dimensional fingerprinting, using the Long strain as the reference. Total RNA extracted from cells infected with the different isolates was hybridized to radiolabeled antisense G or P RNA probes of the Long virus. The RNA:RNA heteroduplexes were digested with RNase A and the resistant products analyzed by gel electrophoresis. Comparative analysis of the cleavage patterns revealed extensive genetic heterogeneity in both genes among viruses isolated in different epidemics. In contrast, 13 viruses isolated in Montevideo during a 3-month period showed much more restricted heterogeneity; thus, 11 viruses represented the predominant type of this outbreak and only 2 other viruses generated different RNA cleavage patterns distantly related to the major type. Statistical analysis of the results obtained indicated progressive accumulation of genetic changes with time along cocirculating evolutionary lineages within the same antigenic subgroup of RS virus. The results are discussed in terms of a model for RS virus evolution.

A single-season epidemic with respiratory syncytial virus subgroup B2 during 10 epidemic years, 1978 to 1988

Respiratory syncytial virus strains isolated from infants and children hospitalized with acute respiratory tract disease in Huntington, W. Va., from July 1979 through June 1988 were categorized by subgroup by using two panels of monoclonal antibodies specific for subgroup A and subgroup B. Of 405 strains tested, 319 (78.8%) were subgroup A, 73 (18.0%) were subgroup B1, and 13 (3.2%) were subgroup B2. The subgroup B2 strains occurred as a single-season epidemic during the epidemiologic year July 1980 to June 1981, except for one strain isolated in the epidemiologic year 1978 to 1979. Subgroup B strains were associated with significantly fewer bronchiolitis illnesses than subgroup A strains. The severity of illnesses caused by subgroup B1 and B2 strains was the same.

Occurrence of respiratory syncytial virus subtypes in hospitalized children in Cleveland, Ohio from 1985 to 1988

In order to determine the frequency of occurrence of the two respiratory syncytial virus (RSV) subtypes in hospitalized children in Cleveland, Ohio, we analyzed clinical isolates obtained during three consecutive winter epidemic seasons between 1985 and 1988. RSV was recovered from the frozen clinical specimens of 197 patients: 176 subtype A, and 21 subtype B. Subtype A predominated during all three epidemic seasons, ranging from 83 to 94% of isolates. We surveyed the clinical records of 16 children with subtype B, and 101 children with subtype A infections, hospitalized at the University Hospitals of Cleveland during these winter epidemics and found no differences in age, sex, race, or clinical spectrum of severity of disease caused by the two subtypes. In contrast to previously reported data, subtype A predominated in each of the winter seasons studied within this community. We conclude that both subtypes circulate concurrently within the community during the winter. In hospitalized children both subtypes appear to cause a similar spectrum of disease. Both the concurrent circulation of RSV subtypes and the similar spectrum of illness pose for important considerations in the development of effective vaccines against this common respiratory agent in children.

Differentiation of respiratory syncytial virus subgroups with cDNA probes in a nucleic acid hybridization assay

A new approach to respiratory syncytial (RS) virus subgroup determination was developed by using a simple nucleic acid filter hybridization technique. By this method, virus-infected cells are bound and fixed in a single step, and the viral RNA in the fixed-cell preparation is characterized directly by its ability to hybridize to cDNA probes specific for either the A or B subgroups of RS virus. The subgroup-specific probes were constructed from cDNA clones that corresponded to a portion of the extracellular domain of the RS virus G protein of either a subgroup B RS virus (8/60) or a subgroup A RS virus (A2). The cDNA probes were labeled with 32P and used to analyze RS virus isolates collected over a period of three decades. Replicate templates of infected cell preparations were hybridized with either the subgroup A or B probe. The subgroup assignments of 40 viruses tested by nucleic acid hybridization were in agreement with the results of subgroup determinations based on their reactivities with monoclonal antibodies, which previously has been the only method available for determining the subgroup classification of RS virus isolates. The nucleic acid hybridization assay has the advantage of providing broad-based discrimination of the two subgroups on the basis of nucleic acid homology, irrespective of minor antigenic differences that are detected in assays in which monoclonal antibodies are used. The nucleic acid hybridization technique provides a reliable method for RS virus subgroup characterization.