Invasive Streptococcus pneumoniae infection in Latin American children: results of the Pan American Health Organization Surveillance Study

Protein-polysaccharide conjugate vaccines against Streptococcus pneumoniae promise to be an effective public health intervention for children, especially in an era of increasing antimicrobial resistance. To characterize the distribution of capsular types in Latin America, surveillance for invasive pneumococcal infection in children < or = 5 years of age was done in six countries between February 1993 and April 1996. Fifty percent of 1,649 sterile-site isolates were from children with pneumonia, and 52% were isolated from blood. The 15 most common of the capsular types prevalent throughout the region accounted for 87.7% of all isolates. Overall, 24.9% of isolates had diminished susceptibility to penicillin: 16.7% had intermediate resistance and 8.3% had high-level resistance. Three customized vaccine formulas containing 7, 12, and 15 capsular types were found to have regional coverages of 72%, 85%, and 88%, respectively. This study emphasizes the need for local surveillance for invasive pneumococcal disease prior to the development and evaluation of protein-polysaccharide conjugate vaccines for children.

Serogroup-specific epidemiology of Streptococcus pneumoniae: associations with age, sex, and geography in 7,000 episodes of invasive disease

A study sample of 7,010 episodes of invasive Streptococcus pneumoniae disease was obtained by combining 13 existing datasets. Disease episodes due to each of 12 pneumococcal serogroups (1, 3-9, 14, 18, 19, and 23) were then compared with episodes in a constant internal control group to describe serogroup-specific variations in disease frequency by age, sex, and geographic origin. The results are presented as odds ratios (with 95% confidence intervals) derived by logistic regression, with adjustment for the major confounders, including dataset of origin. Variation in the male:female ratios between serogroups is small, suggesting that capsular characteristics are an unlikely explanation for the male preference of S. pneumoniae. Serogroups associated with higher nasopharyngeal prevalence (e.g., 19 and 24) are relatively more common in Europe and North American, while the invasive serotypes 1 and 5 are much more common in South America. The custom of reporting serogroup frequencies in two age groups, children and adults, conceals much of the variation in the age distributions across the whole span of life. The reduction of risk associated with serogroups 6, 14, 18, 19, and 23 beyond childhood follows different gradients, being most abrupt in serogroups 14 and most gradual in serogroup 18. The relative risk of disease with serotype 1 declines steadily throughout life, while with serotypes 3 and 8 it increases over middle age. Serogroups 7 and 23 are found unusually frequently in the third decade of life. Because of the wide differences in the epidemiology of individual serogroups of S. pneumoniae, it is questionable whether pneumococcal infection should continue to be classified as a single disease entity.

Molecular epidemiology of adenovirus acute lower respiratory infections of children in the south cone of South America (1991-1994)

A collection of 165 adenovirus strains isolated from nasopharyngeal aspirates of children hospitalized for acute lower respiratory infection in Argentina, Chile, and Uruguay between 1991 and 1994 was studied by restriction enzyme analysis (work performed in the Department of Virology, University of Umeå). Of the isolates, 71% (n = 117) were identified as members of subgenus B. Of these, 101 (61.2%) corresponded to genome type 7h, four (2.4%) to genome type 3p2, four (2.4%) to genome type 11a, one (0.6%) to genome type 7b, and one (0.6%) to genome type 7c. Two isolates that were neutralized as serotype 3 and four isolates that were neutralized as serotype 7 exhibited novel BamHI cleavage profiles corresponding to three new genome types denominated 3x, 7i, and 7j. Subgenus C members represented 28.5% of all typed isolates. Five different genome types of Ad1, seven genome types of Ad2, and three genome types of Ad5 were identified of, which two, two, and one, respectively, were found to correspond to new DNA variants. Only one isolate (0.6%) corresponded to Ad4 of subgenus E. Ad7h was isolated from 17 of the 18 fatal cases recorded among the patients included in the study.

[Determination of bactericidal antibodies directed against vibrio cholerae in an adult population in Montevideo]

Uruguay is the only Latinoamerican country that remains free of cholera. Thus, to obtain a baseline for future diagnosis vibriocidal antibodies were investigated in 100 sera from blood donors serogroup "O". The reaction was carried out in microplates with live antigen Ogawa VC 12. In 95% of sera, titers were below 160, suggesting a high degree of susceptibility to V. cholerae in the population.

Evolutionary pattern of human respiratory syncytial virus (subgroup A): cocirculating lineages and correlation of genetic and antigenic changes in the G glycoprotein

The genetic and antigenic variability of the G glycoproteins from 76 human respiratory syncytial (RS) viruses (subgroup A) isolated during six consecutive epidemics in either Montevideo, Uruguay, or Madrid, Spain, have been analyzed. Genetic diversity was evaluated for all viruses by the RNase A mismatch cleavage method and for selected strains by dideoxy sequencing. The sequences reported here were added to those published for six isolates from Birmingham, United Kingdom, and for two reference strains (A2 and Long), to derive a phylogenetic tree of subgroup A viruses that contained two main branches and several subbranches. During the same epidemic, viruses from different branches were isolated. In addition, closely related viruses were isolated in distant places and in different years. These results illustrate the capacity of the virus to spread worldwide, influencing its mode of evolution. The antigenic analysis of all isolates was carried out with a panel of anti-G monoclonal antibodies that recognized strain-specific (or variable) epitopes. A close correlation between genetic relatedness and antigenic relatedness in the G protein was observed. These results, together with an accumulation of amino acid changes in a major antigenic area of the G glycoprotein, suggest that immune selection may be a factor influencing the generation of RS virus diversity. The pattern of RS virus evolution is thus similar to that described for influenza type B viruses, expect that the level of genetic divergence among the G glycoproteins of RS virus isolates is the highest reported for an RNA virus gene product.

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.

Acute respiratory infections in children from a deprived urban population from Uruguay

To obtain base line data on incidence, duration, clinical characteristics and etiology of acute respiratory infections (ARI), 276 children from deprived families living in Montevideo were followed during 32 months. The target population was divided into two groups for the analysis of the results: children aged less than 12 months and those older than this age. During the follow-up period 1.056 ARI episodes were recorded. ARI incidence was 5.2 per child/year. It was 87% higher in infants than in the older group, as was the duration of the episodes. Most of the diseases were mild. Tachypnea and retractions were seldom observed, but 12 children were referred to the hospital, and 2 infants died. Viral etiology was identified in 15.3% of the episodes. RSV was the predominant agent producing annual outbreaks. Moderate to heavy colonization of the upper respiratory tract by Streptococcus pneumoniae (32.3%) and Hemophilus sp. (18.9%) was recorded during ARI episodes. This community-based study furnish original data on ARI in Uruguay. It enabled to assess the impact of these infections on childhood.

Difficulties encountered in a community-based study of acute respiratory infections in Uruguay

A cohort study on acute respiratory infections, involving 270 children observed by pediatricians in their homes every 10 days over a period of 32 months, gave the opportunity to experience logistic and methodological problems seldom described in the literature. The purpose of this article is to alert researchers as to the difficulties faced when performing community-based studies in developing countries. Although a carefully planned project was undertaken, problem areas included the establishment of the target population, population dynamics, field related problems, laboratory aspects and data management. It is hoped that other investigators may benefit from the extensive experience gained from our program in foreseeing and coping with the difficulties involved.

Evaluation of immunoglobulin E-specific antibodies and viral antigens in nasopharyngeal secretions of children with respiratory syncytial virus infections

Enzyme immunoassays were developed to detect the presence of specific immunoglobulin E (IgE) antibodies and respiratory syncytial (RS) virus structural proteins in nasopharyngeal secretions in order to improve the knowledge on some aspects of the pathogenesis of severe acute lower respiratory tract infections caused by RS virus. These assays were used to analyze clinical specimens from children with RS virus-associated infections (bronchiolitis and pneumonia), and the findings were correlated with the patients' clinical symptoms. The results indicate the presence of specific IgE against the two external glycoproteins (G and F) and the absence of detectable IgE levels for the internal viral antigens. There was a correlation between the levels of IgE-specific antibodies and the amount of viral protein F in the secretions, indicating that the IgE response against the viral glycoproteins might be related to the antigen load. In addition, a correlation was found between higher levels of both viral protein F-specific IgE and F antigen with higher respiratory rates in children with pneumonia. These findings may be relevant because they suggest an association between the virus load and the immune response in the pathogenesis of RS virus infections.

Genome type analysis of South American adenoviruses of subgenus C collected over a 7-year period

A collection of 148 adenovirus strains of subgenus C collected in Argentina, Chile, and Uruguay were studied by restriction enzyme analysis of genomic DNA with endonucleases BamHI, BglII, BstEII, EcoRI, HindIII, KpnI, and SmaI. Only strains corresponding to serotypes 1, 2, and 5 were identified representing both already described and new genome types. The most frequently detected type was Ad 2 followed by Ad 1 and Ad 5. Three different genomic variants of both Ad 1 and Ad 5 were discriminated. Ad 2 with 9 genome types exhibited the greatest variability. Novel profiles emerged only in strains corresponding to this serotype by restriction with BglII and BstEII. The circulation of prototype-like strains of Ad 1 throughout the study period is note-worthy. Thirty-six of 43 strains corresponded to genome type D 1. Clearly, one genome type of each serotype predominated over the 7-year period (Ad 1 D 1, n = 36; Ad 2 D 5, n = 32, Ad 5 D 36, n = 17). Some genomic variants were detected sporadically and only in Argentina, Chile, or Uruguay whereas others were widely distributed and circulated for years. A high proportion of the analysed strains was isolated from children under one year and males were more frequently infected than females.

Colonizing and invasive strains of Streptococcus pneumoniae in Uruguayan children: type distribution and patterns of antibiotic resistance

For the first time in Uruguay the frequency of moderate to heavy colonization of the upper respiratory tract by Streptococcus pneumoniae was investigated in children with acute respiratory infections (n = 717) and in healthy controls (n = 564). Serotypes of S. pneumoniae were identified as colonizing and invasive strains and their susceptibility to antibiotics was determined. Semiquantitative cultures of nasopharyngeal aspirates yielded 42.1% of positives in ambulatory patients and 15.2% in controls. Throat swabs from hospitalized children and matched controls revealed, respectively, 18.4 and 11.5% colonization. Different sampling and culture procedures were evaluated. Seasonal variations in colonization were also detected. Geographic variations in serotype frequency and distribution were assessed. Serotype 14 was predominant among invasive and colonizing strains in patients. Ten serotypes, included in the 23-valent S. pneumoniae vaccine, were not detected. Intermediate resistance to penicillin was seldom observed, but 37.2% of the invasive strains were resistant to cotrimoxazole, indicating the need for a permanent surveillance of isolates to antibiotic susceptibility.

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.

Identification of viruses in a study of acute respiratory tract infection in children from Uruguay

For the purpose of identifying viral agents associated with acute respiratory tract infections (ARI) in children less than 5 years old, a longitudinal community study was undertaken in Montevideo, Uruguay, from May 1985 to December 1987. This report includes results obtained by cell culture and immunofluorescence techniques for detection of respiratory syncytial virus (RSV), influenza A and B viruses, parainfluenza 1 and 3 viruses, and adenovirus. Two populations were studied: children visited at home by pediatricians (group 1) and children with an ARI episode who attended an outpatient clinic (group 2). Nasopharyngeal aspirates were obtained at the time of an ARI episode: 858 from group 1 and 488 from group 2. Viruses were identified in 15.3% of group 1 specimens and in 17.6% of group 2 specimens. RSV was the most frequently recovered agent, accounting for 67.9% and 58.1%, respectively, of all viruses detected. The sensitivity and specificity of RSV isolation by cell culture are compared with detection by indirect immunofluorescence.

A community-based study of acute respiratory tract infections in children in Uruguay

Acute respiratory tract infection (ARI) was investigated in children less than 5 years old in a longitudinal community-based study of 166 families living in a socioeconomically depressed area in Montevideo, Uruguay. Pediatricians made home visits every 10 days from May 1985 to December 1987, and symptoms and signs of ARI were recorded. The incidence of ARI was 5.8 episodes per child-year during the first 12 months of life and decreased with increasing age of the index children; the rate was highest in children 1-5 months old. Children observed from birth were ill during 21% of the visits. According to the definitions of the study, the incidence of lower respiratory tract infection was 11.6% higher than the incidence of upper respiratory tract infections. The rates of ARI were higher during the colder months. Most risk factors for ARI were only marginally statistically significant.

Microbial agents associated with pneumonia in children from Uruguay

The etiology of severe pneumonia, not frequently encountered in a community-based study, was determined in 204 hospitalized children less than 5 years of age. Potential pathogens were identified in 41% of episodes. Viruses were isolated or antigen was detected in 36.3% of cases; 82.4% of these cases were due to respiratory syncytial virus. Bacteria or bacterial antigens were identified in 13.2% of cases; Streptococcus pneumoniae and Haemophilus influenzae were the most frequently identified bacterial pathogens isolated from blood and/or pleural effusions. Mixed infections were identified in 4.9% of the episodes. Among the 17 patients with pleural effusion whose pleural space was drained, the etiology was suggested for 10 (58.8%). A clear-cut seasonal variation was seen, with the highest prevalence between May and October. Viral infections were more common in the first 6 months of life, although viral and bacterial infections were distributed throughout the first 5 years of life.

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

The occurrence of subgroup A and B strains of respiratory syncytial virus (RSV) was studied during three epidemic years, 1985 to 1987, in Uruguay. A set of monoclonal antibodies was selected according to their reactivity with local RSV isolates and used for the typing of RSV directly in nasopharyngeal cells by indirect immunofluorescence. Of 77 specimens, 69 could be typed as belonging to subgroup A or B, 5 could not be typed with the restricted set of monoclonal antibodies employed, and 3 reacted with both subgroup-specific antibodies. In 1985 and 1986 subgroup A predominated, accounting for 65.7% of all typed specimens, but in 1987 subgroup B surpassed subgroup A, accounting for 82.4% of the samples.

[Comparison between immunofluorescence and immunoenzymatic assay for the rapid diagnosis of the respiratory syncytial virus in nasopharyngeal secretions]

An enzyme immunoassay, RSV-EIA Abbot, was evaluated by comparison with indirect immunofluorescence. Nasopharyngeal secretions obtained from 95 infants and young children with acute respiratory infections were examined for the presence of respiratory syncytial virus antigens with both methods. Specimens were stored at -70 degrees C before being tested by EIA. Out of 60 samples positive by indirect immunofluorescence, 46 were also positive by RSV-EIA (sensitivity 78.7%) and 34 out of 35 immunofluorescence negative specimens were negative by RSV-EIA (specificity 97.1%). Therefore, the EIA appears to be an acceptable test for the rapid detection of RSV as an alternative for indirect immunofluorescence.

[Antigenic variants of the respiratory syncytial virus in Argentina and Uruguay]

The characterization of RSV antigenic variants was carried out on 160 nasopharyngeal aspirates from children under 5 years of age, from Argentina and Uruguay, with acute respiratory infection and a previously positive etiological diagnosis for RSV. Results for Argentina were: 20.9% of samples belonged to subtype A, 76.9% to subtype B and the remaining 2.2% to new subtypes as yet uncharacterized. Results for Uruguay were: 5.6% of samples belonged to subtype A, 81% to subtype B and 13.5% to other subtypes. Subtype B was predominant in both countries. The correlation of RSV antigenic variants with the clinical picture and epidemiological profile is currently underway.