Respiratory syncytial virus infection in human immunodeficiency virus-infected children

Respiratory syncytial virus immunoprophylaxis: Novel opportunities and a call for equity

With the approval of the first vaccines against respiratory syncytial virus (RSV) and a novel RSV-neutralizing antibody, 2023 has been perceived as a game-changing year in preventing severe outcomes of RSV infections in infants and the elderly. However, the costs of these pharmaceuticals are high, while RSV disproportionately impacts populations of low-to-middle-income regions, which may continue to suffer from a lack of pharmaceutical measures for RSV prevention under health and socioeconomic disparities. This paper presents an overview of the characteristics, clinical results, and approval status of various RSV vaccines and anti-RSV antibodies. It posits that wealthy nations cannot monopolize RSV immunoprophylaxis and should work jointly to make it available to lower-income countries. An approach toward RSV immunoprophylaxis equity based on five points is offered: (1) integration of RSV vaccines and antibodies into the existing global humanitarian distribution systems, (2) using affordable RSV vaccine pricing models, (3) enforcing equity as a part of national and global public health strategy, (4) implementing equitable allocation frameworks for RSV immunoprophylaxis, and (5) promoting local manufacturing. Such a plan needs to be put into action as soon as possible to avoid delays in serving the populations with the highest needs related to RSV burden.

Respiratory syncytial virus infection: why does disease severity vary among individuals?

Introduction: Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory tract infections in infancy. While many infants are infected with RSV, the nature and severity of the disease vary among individuals. RSV causes bronchiolitis, pneumonia, and asthma exacerbation. However, most children infected with RSV have only mild upper airways disease and may be asymptomatic.Areas covered: Despite efforts to elucidate mechanisms for the various clinical responses to RSV infection, they remain largely unknown, suggesting that susceptibility and disease are influenced by multiple intrinsic and extrinsic factors. This article reviews the available literature on the field of RSV disease severity and discusses important factors associated to susceptibility and different disease outcome.Expert opinion: The severity of RSV-induced illness is a phenomenon that depends on a variety of graded mechanisms of interaction between the host, virus, and environment. This may lead to differences in the intensity of immune response in the lung and different courses of the disease. By characterizing, classifying, and grading the affecting factors in high-risk patients versus those who do not fall ill by RSV, we may find therapies or point to disease-limiting medications.

Risk stratification of immunocompromised children, including pediatric transplant recipients at risk of severe respiratory syncytial virus disease

BACKGROUND

Respiratory syncytial virus (RSV) infection is associated with increased morbidity and mortality in immunocompromised patients. Our goal was to develop a framework for risk stratifying immunocompromised patients, including transplant patients, for RSV prophylaxis.

METHODS

Risk factors for severe RSV disease in immunocompromised patients were identified in the literature and by an expert panel via survey. Experts assigned a probability of developing severe disease (0 to 100 scale) to the risk factors for each immunocompromised population. The results were validated using a clinical dataset. Linear mixed models adjusted for within-expert clustering of ranks were used to estimate average scores, and differences were tested using paired t tests. Logistic regression was utilized to identify important determinants of severe RSV disease.

RESULTS

The survey was emailed to twenty-seven experts and thirteen responded (48%). Across all transplant groups, age <2 years (mean 77.1, 95% CI 71.7, 82.5) and day care attendance (mean 72.8, 95% CI 67.3, 78.3) were assigned the highest risk of severe disease. The highest risk groups were lung transplant recipients (mean 73.2, 95% CI 67.6, 78.8), combined lung and heart transplant recipients (mean 75.2, 95% CI 69.6, 80.7), allogeneic stem cell transplant (mean 76.0, 95% CI 70.4, 81.6), and severe combined immunodeficiency (mean 74.7, 95% CI 69.1, 80.3).

CONCLUSION

The results provide a logical validity to current practice and provide guidance for prioritizing patients to receive prophylactic agents to prevent severe RSV disease. The results will facilitate the development of a risk stratification tool for RSV prophylaxis for immunocompromised patients.

Respiratory syncytial virus prophylaxis and the "special population"

Bronchiolitis is the most frequent airway infection in the first 2 years of life, and the respiratory syncytial virus (RSV) is the most frequently responsible virus. In selected high-risk groups, RSV may cause severe respiratory disease leading to hospitalization, need for mechanical ventilation, and even death. These high-risk groups include children with congenital heart disease, infants with neuromuscular impairment, cystic fibrosis, Down Syndrome, immunodeficiency syndromes and others specific conditions. In these high-risk populations defined in literature as "special population", a 3- to 10-fold increase in the rate of RSV hospitalization has been observed, justifying RSV specific prophylaxis with palivizumab, a monoclonal antibody that binds a viral glycoprotein epitope and blocks the link between RSV and target cell. Evidence of safety and efficacy of RSV prophylaxis in these populations is lacking. Given the low incidence of these conditions, randomized clinical trials are not feasible. The purpose of this paper is to give an update from the literature of various conditions at higher risk to develop severe RSV infection, and to offer an overview of the efficacy of palivizumab in preventing RSV infection in these specific populations.

Biomarkers of respiratory syncytial virus (RSV) infection: specific neutrophil and cytokine levels provide increased accuracy in predicting disease severity

Despite fundamental advances in the research on respiratory syncytial virus (RSV) since its initial identification almost 60 years ago, recurring failures in developing vaccines and pharmacologic strategies effective in controlling the infection have allowed RSV to become a leading cause of global infant morbidity and mortality. Indeed, the burden of this infection on families and health care organizations worldwide continues to escalate and its financial costs are growing. Furthermore, strong epidemiologic evidence indicates that early-life lower respiratory tract infections caused by RSV lead to the development of recurrent wheezing and childhood asthma. While some progress has been made in the identification of reliable biomarkers for RSV bronchiolitis, a "one size fits all" biomarker capable of accurately and consistently predicting disease severity and post-acute outcomes has yet to be discovered. Therefore, it is of great importance on a global scale to identify useful biomarkers for this infection that will allow pediatricians to cost-effectively predict the clinical course of the disease, as well as monitor the efficacy of new therapeutic strategies.

Increased Rates of Respiratory and Diarrheal Illnesses in HIV-Negative Persons Living With HIV-Infected Individuals in a Densely Populated Urban Slum in Kenya

BACKGROUND

Prolonged pathogen shedding and increased duration of illness associated with infections in immunosuppressed individuals put close human immunodeficiency virus (HIV)-negative contacts of HIV-infected persons at increased risk of exposure to infectious pathogens.

METHODS

We calculated incidence and longitudinal prevalence (number of days per year) of influenzalike illness (ILI), diarrhea, and nonspecific febrile illness during 2008 from a population-based surveillance program in the urban slum of Kibera (Kenya) that included 1830 HIV-negative household contacts of HIV-infected individuals and 13 677 individuals living in exclusively HIV-negative households.

RESULTS

For individuals ≥5 years old, incidence was significantly increased for ILI (risk ratio [RR], 1.47; P < .05) and diarrhea (RR, 1.41; P < .05) in HIV-negative household contacts of HIV-infected individuals compared with exclusively HIV-negative households. The risk of illness among HIV-negative persons was directly proportional to the number of HIV-infected persons living in the home for ILI (RR, 1.39; P < .05) and diarrhea (RR, 1.36; P < .01). We found no increased rates of illness in children <5 years old who lived with HIV-infected individuals.

CONCLUSIONS

Living with HIV-infected individuals is associated with modestly increased rates of respiratory and diarrheal infections in HIV-negative individuals >5 years old. Targeted interventions are needed, including ensuring that HIV-infected persons are receiving appropriate care and treatment.

High risk for RSV bronchiolitis in late preterms and selected infants affected by rare disorders: a dilemma of specific prevention

Respiratory syncytial virus (RSV) is the most frequent aetiologic agent that causes bronchiolitis and lower respiratory tract infection in infants. These infections may be severe and even life-threatening in selected high-risk populations. Traditional, well-established, high-risk populations are preterm infants with or without chronic lung disease and children with congenital heart disease. For these children, RSV prophylaxis using palivizumab, a monoclonal anti-RSV humanised antibody against the F-protein of RSV, has proven safe and efficacious in preventing RSV-related hospitalisation. Recently, a number of rare medical conditions have been associated with the risk of severe RSV infections. Evidence of safety and efficacy of RSV prophylaxis in these populations is lacking. Given the low incidence of these conditions, randomised trials are not feasible. A practical, opinion-based approach to this dilemma is offered in this paper. It is proposed that these rare disorders may qualify for RSV prophylaxis if the association between a specific condition and the risk of severe RSV infection is confirmed in at least 3 independent publications, of which at least 1 includes a prospective cohort study. To facilitate pharmaco-economic analyses, at least one of the three studies must also report on the absolute risk of severe RSV infection in the specified illness. The authors believe that qualification criteria will enable caregivers to target RSV prophylaxis more effectively in children with rare conditions and the proposed approach provides direction for future epidemiological studies on the risk of severe RSV infection in children with these uncommon, medical illnesses.

Epidemiology and prevention of respiratory syncytial virus infections among infants and young children

Since its discovery in 1956, respiratory syncytial virus (RSV) has been recognized as one of the most common causes of serious lower respiratory tract infections in young children worldwide. While considered a high priority, development of a safe and effective vaccine has remained elusive. Prevention of RSV disease relies on infection control and hygiene measures, as well as providing immunoprophylaxis in select infants. The prophylaxis, however, is costly, and so targeting the recipient population and timing of administration is important for optimal effectiveness and judicious use of limited health care resources. This article reviews the epidemiology of RSV infections in infants and young children, including risk factors for severe disease, so as to inform decisions about prevention efforts.

Respiratory syncytial virus prevention and therapy: past, present, and future

Respiratory syncytial virus (RSV) is the most common respiratory pathogen in infants and young children worldwide. More than 50 years after its discovery, and despite relentless attempts to identify pharmacological therapies to improve the clinical course and outcomes of this disease, the most effective therapy remains supportive care. Although the quest for a safe and effective vaccine remains unsuccessful, pediatricians practicing during the past decade have been able to protect at least the more vulnerable patients with safe and effective passive prophylaxis. This review summarizes the history, microbiology, epidemiology, pathophysiology, and clinical manifestations of this infection in order to provide the reader with the background information necessary to fully appreciate the many challenges presented by the clinical management of young children with bronchiolitis. The last part of this article attempts an evidence-based review of the pharmacologic strategies currently available and those being evaluated, intentionally omitting highly experimental approaches not yet tested in clinical trials and, therefore, not likely to become available in the foreseeable future.

Immunoprophylaxis and immunotherapy: role in the prevention and treatment of repiratory syncytial virus

It is now apparent that neutralizing antibody may play an important role in ameliorating RSV lower repiratory tract illness. At the present time immunoprophylaxis and immunotherapy with polyclonal antibodies show the most promise in the prevention and treatment of RSV illness. Several questions remained to be answered. These include the practical application of IGIV in prevention and treatment of RSV illness. Intravenous lines are often difficult to place and maintain. With the further development of polyclonal or monoclonal antibodies it may be possible to immunize prospective donors and boost their anti RSV titers to the degree that a hyper-immune IGIV with sufficient antibody to be given intramuscularly could be produced. The role for RSV-specific monoclonal antibodies for disease prevention or treatment must be defined as well as the appropriatee viral epitopes to target. In the absence of a safe and effective vaccine, it is clear that, despite these questions passive immunotherapy and immunoprophylaxis offers the greatest hope for the prevention and treatment of RSV disease in high risk infants and children.

Respiratory viral infections in infants: causes, clinical symptoms, virology, and immunology

In global terms, respiratory viral infection is a major cause of morbidity and mortality. Infancy, in particular, is a time of increased disease susceptibility and severity. Early-life viral infection causes acute illness and can be associated with the development of wheezing and asthma in later life. The most commonly detected viruses are respiratory syncytial virus (RSV), rhinovirus (RV), and influenza virus. In this review we explore the complete picture from epidemiology and virology to clinical impact and immunology. Three striking aspects emerge. The first is the degree of similarity: although the infecting viruses are all different, the clinical outcome, viral evasion strategies, immune response, and long-term sequelae share many common features. The second is the interplay between the infant immune system and viral infection: the immaturity of the infant immune system alters the outcome of viral infection, but at the same time, viral infection shapes the development of the infant immune system and its future responses. Finally, both the virus and the immune response contribute to damage to the lungs and subsequent disease, and therefore, any prevention or treatment needs to address both of these factors.

Severe respiratory syncytial virus (RSV) infection in infants with neuromuscular diseases and immune deficiency syndromes

Respiratory syncytial virus (RSV) is an important cause of lower respiratory tract infection (LRTI) in infants and children. There is growing evidence of severe RSV disease in infants with neuromuscular diseases and immune deficiency syndromes. Factors predisposing to a more severe course of RSV disease in neuromuscular diseases include the impaired ability to clear secretions from the airways due to ineffective cough, respiratory muscle weakness, high prevalence of gastro-oesophageal reflux and swallowing dysfunction which leads to aspiration. Similarly, pulmonary disease is a common presenting feature and complication of T-cell immunodeficiency. Infants with severe congenital and acquired immune deficiency syndromes may demonstrate prolonged viral shedding in RSV LRTI and are reported to have increased morbidity and mortality associated with RSV infection. Although not indicated in most guideline statements, palivizumab prophylaxis for these uncommon underlying conditions is under consideration by clinicians. Prospective studies are needed to determine the burden of RSV disease in these children.

Comparison of cytokine responses in nasopharyngeal aspirates from children with viral lower respiratory tract infections

Aim: To determine whether nasopharyngeal aspirates (NPAs) cytokine response is different according to the causative viruses in children with lower respiratory tract infections (LRTI).

Methods: NPAs from 277 children with LRTI caused by respiratory virus were evaluated. Based on the proven viral agents, LRTI patients were divided into four groups. Levels of IL‐4, IL‐5 and IFN‐γ were determined by ELISA.

Results: Patients with influenza virus infection demonstrated significantly lower IL‐4 and IL‐5 levels than those with other three groups. Patients with respiratory syncytial virus (RSV) infection showed an increase in production of IL‐4 and IL‐5, and a decrease in the IFN‐γ level when compared to patients with influenza virus infection. Interestingly, a similar Th2 response was seen in patients with parainfluenza virus or adenovirus infection.

Conclusion: These results demonstrate that respiratory viruses can induce different local cytokine responses. However, Th2 biased responses are not unique for RSV but seem to be predominant in respiratory viruses of young children.

Respiratory Diseases

Upper respiratory tract infections are the most common type of infectious diseases and a leading cause of outpatient illness (1,2).

Molecular epidemiological analysis of a nosocomial outbreak of respiratory syncytial virus associated pneumonia in a kangaroo mother care unit in South Africa

Respiratory syncytial virus (RSV) may cause severe lower respiratory tract disease in premature infants. Prolonged viral shedding has been reported in patients with underlying immunosuppressive disorders, such as human immunodeficiency virus 1 (HIV-1) infection. During March to May 2006, 23 preterm pediatric patients developed nosocomial pneumonia in a district hospital in the Gauteng Province of South Africa due to RSV infection. The patients were identified using routine diagnostic testing. All had been admitted with their mothers to a Kangaroo Mother Care (KMC) ward from birth--a low care unit for the management of stable low birth weight infants. The HIV-1 seroprevalence among the mothers to these infants was 52.6%, translating to a 52.6% perinatal exposure. A multiplex nested RT-PCR was used to subtype RSV positive nasopharyngeal aspirates. Sequencing and phylogenetic analysis of part of the G-protein gene was used for molecular epidemiological analysis of the outbreak. In total, 19 of the 23 RSV positive specimens could be PCR amplified and sequenced. The subtype A, GA5 genotype was identified in 14 specimens and the BA genotype, a new subtype B genotype not previously recognized in South Africa, in seven. One patient had an infection with both genotypes. Phylogenetic analysis demonstrated eight separate introductions. Two of the strains identified in this outbreak were identical to strains circulating in a general pediatric ward of this hospital during the preceding month. Inadequate infection control measures by health care providers and mothers to children in KMC units may increase potentially the risk of severe RSV infection in a population group with compounded risk factors.

Diagnostic assays for respiratory syncytial virus disease

Respiratory syncytial virus (RSV) infection in the United States and worldwide is a major cause of morbidity and mortality and of outpatient visits, hospitalizations, and increased healthcare costs. Effective diagnosis of viral respiratory infections, as well as recognition and understanding of the benefits and limitations of diagnostic laboratory testing, is essential. Serology is not useful for diagnosing acute respiratory illness. Antigen-based assays are widely available, easy to use, provide rapid results, and are inexpensive; however, they are less sensitive than cell culture utilizing good specimen collection and processing techniques. Cell culture, which was previously considered the gold standard for identification of respiratory viruses, in many settings is being replaced by nucleic acid amplification assays that have even greater sensitivity and provide more rapid results. Although available chiefly at large hospitals and reference laboratories, molecular assays may fulfill the need for more sensitive and rapid diagnosis of illnesses caused by respiratory viruses. The seasonality of RSV as measured by nucleic acid amplification-based assays appears to be broader with better identification of patient populations that harbor RSV between yearly epidemic peaks compared with the seasonality of RSV as measured by the older techniques. As these new diagnostic methodologies emerge, guidelines will be needed to direct their appropriate use in the diagnostic laboratory.

Influenzavirus infection is a primary cause of febrile respiratory illness in HIV-infected adults, despite vaccination

BACKGROUND

There are, to our knowledge, no prospective studies of respiratory tract infections in human immunodeficiency virus (HIV)-infected adults in the highly active antiretroviral therapy (HAART) era. We performed a surveillance study of outpatients who presented with fever and respiratory symptoms to examine the role of viral pathogens in these patients.

METHODS

Consecutive patients with a temperature of >38.0 degrees C and respiratory symptoms were recruited from a tertiary care HIV clinic during the period 2003-2006. Nasal pharyngeal samples were tested for influenzavirus A and B, respiratory syncytial virus, and human metapneumovirus using real-time multiplex polymerase chain reaction assays. Paired acute- and convalescent-phase serum samples were tested for respiratory viruses by complement fixation.

RESULTS

Fifty patients (90% of whom were receiving HAART) were included in the study (median CD4(+) T cell count, 325 cells/microL; median HIV RNA level, <50 copies/mL). A causative pathogen was identified in 25 patients (50%). Even though 76% of subjects had received influenza vaccine, viral infections were diagnosed in 21 patients (42%), as follows: influenza A, 10 patients; influenza B, 10; and parainfluenza virus type 3 infection, 1. Patients with and those without viral infection had similar demographic characteristics and HIV statuses. No patients with influenza and 23% of patients with other conditions had radiography-confirmed pneumonia (P=.07). Antibiotic prescriptions were common: 70% of patients received antibiotics. No patients with influenza required hospitalization, compared with 21% of other patients (P=.03).

CONCLUSIONS

Although illness was mild, influenza accounted for a large proportion of unscheduled visits to a health care provider for respiratory illness and was associated with unnecessary antibiotic prescriptions that may contribute to antimicrobial resistance. Vaccination alone was insufficient to prevent infection. Thus, specific identification and management of influenza should be performed in HIV-infected outpatients who present with fever and respiratory symptoms.

Respiratory virus infection in infants and children

The recent availability of diagnostic polymerase chain reaction-based assays for the detection of viral pathogens has allowed us to identify the infectious agents present in a large percentage of culture-negative specimens. The information gained by these studies has led to a reassessment of the prevalence of individual viruses in lower respiratory tract infections in both normal and immunocompromised children. Pathologic examination of less severe cases identified by more sensitive methodologies in immunocompetent children is now possible and has prompted the realization that many of the classic features of particular viral infections in the lung are in fact hallmarks of fulminant disease. In this article we review the body of literature discussing these anatomic findings, the approaches taken by those investigators, and the types of reagents that are commercially available.

Immunopathology of RSV infection: prospects for developing vaccines without this complication

Respiratory syncytial virus is the most important cause of lower respiratory tract infection in infants and young children. RSV clinical disease varies from rhinitis and otitis media to bronchiolitis and pneumonia. An increased incidence of asthma later in life has been associated with the more severe lower respiratory tract infections. Despite its importance as a pathogen, there is no licensed vaccine against RSV. This is due to a number of factors complicating the development of an effective and safe vaccine. The immunity to natural RSV infection is incomplete as re-infections occur in all age groups, which makes it challenging to design a protective vaccine. Second, the primary target population is the newborn infant, which has a relatively immature immune system and maternal antibodies that can interfere with vaccination. Finally, some vaccines have resulted in a predisposition for exacerbated pulmonary disease in infants, which was attributed to an imbalanced Th2-biased immune response, although the exact cause has not been elucidated. This makes it difficult to proceed with vaccine testing in infants. It is likely that an effective and safe vaccine needs to elicit a balanced immune response, including RSV-specific neutralising antibodies, CD8 T-cells, Th1/Th2 CD4 T-cells and preferably secretory IgA. Subunit vaccines formulated with appropriate adjuvants may be adequate for previously exposed individuals. However, intranasally delivered genetically engineered attenuated or vectored vaccines are currently most promising for newborns, as they are expected to induce a balanced immune response similar to that elicited to natural infection and not be subject to interference from maternal antibodies. Maternal vaccination may be the optimal strategy to protect the very young infants.

Respiratory virus infections in children with cancer or HIV infection

Most studies focusing on respiratory infections in immunocompromised children have been addressed to bacterial etiology. However, respiratory virus infections in this population can also lead to severe disease. The objective of this study is to evaluate the clinical significance of respiratory virus infections in children with cancer or human immunodeficiency virus (HIV) infection. Retrospective study conducted in a teaching hospital in Madrid. Medical records from children <or=14 years diagnosed with cancer or with HIV infection were reviewed. We analyzed demographic characteristics, clinical syndromes associated with the infection, need for hospitalization, treatment prescribed, and outcome. Fifty-three respiratory viral infections were identified: 26 (20%) in 129 HIV-infected children and 27 (12%) in 218 children with cancer. Twenty (38%) of the respiratory infections were nosocomial. Causal viruses were: respiratory syncytial virus, 43%; influenza A, 26%; adenovirus, 13%; parainfluenza virus, 13%; and influenza B, 4%. Thirty-three children were hospitalized: 14 (54%) with HIV infection and 19 (70%) receiving anticancer chemotherapy. Pneumonia occurred in 11 (34%) of the 33 hospitalized children. Four (21%) of the 19 hospitalized children with cancer, but none of the HIV-infected children, were admitted to the Pediatric Intensive Care Unit (P=0.096). Two children with cancer died. Common respiratory virus infections in children with cancer or HIV infection have a relevant morbidity. The fact that 40% of these infections are hospital-acquired emphasizes the need for isolation and preventive measures.

Respiratory Syncytial Virus G Protein and G Protein CX3C Motif Adversely Affect CX3CR1+T Cell Responses

Interactions between fractalkine (CX3CL1) and its receptor, CX3CR1, mediate leukocyte adhesion, activation, and trafficking. The respiratory syncytial virus (RSV) G protein has a CX3C chemokine motif that can bind CX3CR1 and modify CXCL1-mediated responses. In this study, we show that expression of the RSV G protein or the G protein CX3C motif during infection is associated with reduced CX3CR1+ T cell trafficking to the lung, reduced frequencies of RSV-specific, MHC class I-restricted IFN-gamma-expressing cells, and lower numbers of IL-4- and CX3CL1-expressing cells. In addition, we show that CX3CR1+ cells constitute a major component of the cytotoxic response to RSV infection. These results suggest that G protein and the G protein CX3C motif reduce the antiviral T cell response to RSV infection.

Immune responses and disease enhancement during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is one of the commonest and most troublesome viruses of infancy. It causes most cases of bronchiolitis, which is associated with wheezing in later childhood. In primary infection, the peak of disease typically coincides with the development of specific T- and B-cell responses, which seem, in large part, to be responsible for disease. Animal models clearly show that a range of immune responses can enhance disease severity, particularly after vaccination with formalin-inactivated RSV. Prior immune sensitization leads to exuberant chemokine production, an excessive cellular influx, and an overabundance of cytokines during RSV challenge. Under different circumstances, specific mediators and T-cell subsets and antibody-antigen immune complex deposition are incriminated as major factors in disease. Animal models of immune enhancement permit a deep understanding of the role of specific immune responses in RSV disease, assist in vaccine design, and indicate which immunomodulatory therapy might be beneficial to children with bronchiolitis.

Pathogenesis of Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is recognized as the most important cause of serious lower respiratory tract illness in infants and young children worldwide causing repeat infections throughout life with serious complications occurring in the elderly and immune compromised patient. The level of disease pathogenesis associated with RSV infection is balanced between virus elimination and the nature of the immune response to infection. The innate and adaptive immune responses to RSV infection are not fully elucidated; however, significant progress has been made in understanding the virus-host relationship and mechanisms associated with disease pathogenesis. This review summarizes important aspects of these findings, and provides current perspective on processes that may contribute to RSV disease pathogenesis.

Importance of nosocomial respiratory syncytial virus infections in an African setting

OBJECTIVE

To define the importance of nosocomial-acquired respiratory syncytial virus (RSV) infection in an area with a high prevalence of paediatric HIV-1 infection.

METHODS

A prospective study was performed that involved all children hospitalized to a general paediatric ward during the course of an RSV epidemic. These children were screened within 24 h of admission and subsequently at 3-4 day intervals for RSV infection using a direct immunofluorescence assay.

RESULTS

RSV was detected in 36 (11.8%) of the 305 children upon initial investigation. Fourteen (38.9%) of the 36 children with community-acquired RSV infection were HIV-1 infected. Repeat sampling for RSV infection was performed in 130 children who tested negative for RSV infection on initial screening and who were hospitalized for > or =3 days. Nosocomial acquisition of RSV occurred among 11.5% of these children, of whom 33% were HIV-1 infected. Fourteen (93.3%) of the children with nosocomial RSV acquisition were clinically symptomatic and treated for 'nosocomial-sepsis'. Furthermore, RSV was isolated from 54% of all children who were investigated for clinically diagnosed nosocomial sepsis. Two (13%) of 15 children with nosocomial RSV infection died; both had other underlying medical conditions.

CONCLUSION

RSV is an important under-recognized cause of nosocomial infection and sepsis among children in this African country. Active interventions are warranted in addressing this problem, as has been successfully undertaken in developed countries.

Selected populations at increased risk from respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the principal cause of bronchiolitis and pneumonia in infants and young children worldwide. Deficits in cellular immunity appear to promote severe RSV disease in children with malignancies, those undergoing chemotherapy and bone marrow transplant recipients. Respiratory syncytial virus infection appears to exacerbate pulmonary symptoms of cystic fibrosis. In such patients RSV disease may result in a prolonged hospital course, which is often complicated by the need for mechanical ventilation. Retrospective analyses of hospital admissions for RSV bronchiolitis among Native American and Alaskan Native children younger than 1 year of age have demonstrated rates of 62 per 1000 or higher, compared with the national average of 34 per 1000. Among these ethnic groups, specific host factors as well as environmental factors appear to contribute to these comparatively high rates of hospitalization for RSV infection. Respiratory syncytial virus has the potential to cause disease in all age groups. A 3-year observational study found that individuals who lived in a community setting, or who cared for young children on a consistent basis, experienced acute respiratory infections more commonly than those living independently or whose interaction with children was limited.

Ineffectiveness of trimethoprim-sulfamethoxazole prophylaxis and the importance of bacterial and viral coinfections in African children with Pneumocystis carinii pneumonia

African human immunodeficiency virus type 1 (HIV-1)-infected children were evaluated to define the burden of Pneumocystis carinii pneumonia (PCP) and its interaction with bacterial and viral pathogens. P. carinii was identified in 101 (43.7%) of 231 episodes of pneumonia among 185 HIV-1-infected children (median age, 4.5 months; range, 1.7-27.3 months). Receipt of trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis was not associated with a significant reduction (36%; 95% confidence interval [CI], -15.4% to 64.5%) in isolation of P. carinii among children considered to have received adequate prophylaxis (37.7% of children) compared with children who had never received any prophylaxis (48.5% of children). However, deaths among children with PCP who had been taking TMP-SMX prophylaxis were markedly reduced (98.6%; 95% CI, 89.1%-99.8%) compared with children who were not taking prophylaxis. Concurrent P. carinii infection was observed in 6 of 18, 11 of 26, and 4 of 6 HIV-1-infected children who had bacteremia, a respiratory virus isolated, or Mycobacterium species isolated, respectively.

Immune response to respiratory syncytial virus in young Brazilian children

We have evaluated the cellular and humoral immune response to primary respiratory syncytial virus (RSV) infection in young infants. Serum specimens from 65 patients <=12 months of age (39 males and 26 females, 28 cases <3 months and 37 cases > or = 3 months; median 3 3.9 months) were tested for anti-RSV IgG and IgG subclass antibodies by EIA. Flow cytometry was used to characterize cell surface markers expressed on peripheral blood mononuclear cells (PBMC) from 29 RSV-infected children. There was a low rate of seroconversion in children <3 months of age, whose acute-phase PBMC were mostly T lymphocytes (63.0 +/- 9.0%). In contrast, a higher rate of seroconversion was observed in children >3 months of age, with predominance of B lymphocytes (71.0 +/- 17.7%). Stimulation of PBMC with RSV (2 x 10(5) TCID50) for 48 h did not induce a detectable increase in intracellular cytokines and only a few showed a detectable increase in RSV-specific secreted cytokines. These data suggest that age is an important factor affecting the infants' ability to develop an immune response to RSV.

Respiratory syncytial virus--viral biology and the host response

Respiratory syncytial virus (RSV) is the most important cause of respiratory tract infection in infants. We have an incomplete understanding of the reasons why some infants are more severely affected by RSV than others. There is no effective antiviral treatment for the infection. Advances in our understanding of the biology of RSV, particularly in relation to the attachment protein G and the fusion protein F, have revealed potential targets for new antiviral therapies and vaccine development. In response to RSV infection an intense inflammatory response is triggered, mediated initially by the infected airway epithelial cells. Cell mediated responses are important in controlling the extent of infection and in viral clearance. Humoral responses are important in protection. There is early evidence that genetic variation of the host response can influence the outcome of RSV-induced bronchiolitis.

Severe respiratory syncytial virus pneumonia associated with primary Epstein-Barr virus infection

This is a case report of a child with severe respiratory syncytial virus (RSV) pneumonia and concurrent infection with Epstein-Barr virus. We hypothesize that immunosuppression due to EBV may have contributed to the severity of his RSV infection. The diagnosis of RSV infection was facilitated by bronchoalveolar lavage.

Lower respiratory tract infections associated with influenza A and B viruses in an area with a high prevalence of pediatric human immunodeficiency type 1 infection

BACKGROUND

Despite the high burden of pediatric HIV-1 infection in developing countries, there are few data on the clinical course of influenza virus-associated lower respiratory tract infection (LRTI) in these children.

OBJECTIVE

To define and compare the clinical course of HIV-1-infected and -uninfected African children hospitalized with influenza virus associated severe LRTI.

METHODS

Children with severe LRTI were prospectively recruited between March, 1997, and March, 1999, as part of a broader study evaluating the etiology and outcome of this condition in hospitalized HIV-1-infected and -uninfected children. The results of children in whom influenza A or B virus was identified by immunofluorescent antibody staining after shell vial culture are reported. Viruses isolated were typed by hemagglutination inhibition assays.

RESULTS

Twenty-five (21.6%) of the 116 children hospitalized with severe LRTI in whom influenza A or B virus was identified were HIV-1-infected. HIV-1-infected children were older than uninfected children (mean age +/- SD 17.4 +/- 10.8 months vs. 10.2 +/- 8.9 months; P = 0.002). HIV-1-infected children were more likely to have an underlying medical illness (in addition to HIV-1 infection) predisposing them to more severe LRTI (32.0% vs. 13.2%; P = 0.03). HIV-infected children were also more likely to have indirect evidence of bacterial coinfection, including chest radiographic evidence of confluent alveolar consolidation (78.9% vs. 35.1%, P = 0.006), and were less likely be wheezing (8.0% vs. 31.9%, P = 0.01). However, there was no difference in the clinical outcome of HIV-1-infected and -uninfected children. The duration of hospitalization [median (range) 5 (2 to 33) days vs. 4 (0 to 21) days, P = 0.08] and the mortality rates (8.0% vs. 2.2%, P = 0.20) were similar between HWV-1-infected and -uninfected children.

CONCLUSION

HIV-1-infected children hospitalized with severe LRTI associated with influenza virus have an outcome similar to that of HIV-1-uninfected children even in the absence of antiretroviral or anti-influenza virus treatment.

Differing manifestations of respiratory syncytial virus-associated severe lower respiratory tract infections in human immunodeficiency virus type 1-infected and uninfected children

BACKGROUND

Respiratory syncytial virus (RSV) causes increased morbidity and mortality in immunocompromised children. The outcome of RSV-associated lower respiratory tract infections (LRTI) in HIV-infected children, is less well described.

METHODS

Children from a prospective study evaluating the etiology of

Increased burden of respiratory viral associated severe lower respiratory tract infections in children infected with human immunodeficiency virus type-1

OBJECTIVES

To determine the burden of viral associated severe lower respiratory tract infections (SLRTI) in human immunodeficiency virus-infected (HIV+) and HIV-uninfected (HIV-) urban black South African children.

METHODS

Children with SLRTI aged 2 to 60 months were enrolled between March 1997 and March 1998. Monoclonal antibody immunofluorescent testing was performed on nasopharyngeal aspirates to detect respiratory syncytial virus (RSV), influenza A and B, parainfluenza 1-3, and adenovirus-specific antigens.

RESULTS

Of the 990 children studied, 44.6% were HIV+. The estimated burden of disease of viral associated SLRTI in children under 2 years was increased for RSV, influenza A/B viruses, parainfluenza 1-3 viruses, and adenovirus in children who were HIV+ compared with children who were HIV- (P <.001). Viral pathogens, however, were identified less frequently (15.7% vs 34.8%, P < 10(-5)) and bacterial pathogens more frequently (12.5% vs 5.8%, P <.0001) in children who were HIV+ than in children who were HIV- and had SLRTI. The seasonal peak for RSV in late summer-early autumn observed in children who were HIV- was less evident in children who were HIV+ (P =.02). Children who were HIV+ and had virus-associated SLRTI had a higher mortality rate (7. 5%) than did children who were HIV- (0%, P < 10(-3)).

CONCLUSIONS

The contribution of viral associated SLRTI differs between HIV+ and HIV- children. In HIV+ children in South Africa, RSV isolation is not limited by season.

Respiratory syncytial virus infection: immune response, immunopathogenesis, and treatment

Respiratory syncytial virus (RSV) is the single most important cause of lower respiratory tract infection during infancy and early childhood. Once RSV infection is established, the host immune response includes the production of virus-neutralizing antibodies and T-cell-specific immunity. The humoral immune response normally results in the development of anti-RSV neutralizing-antibody titers, but these are often suboptimal during an infant's initial infection. Even when the production of RSV neutralizing antibody following RSV infection is robust, humoral immunity wanes over time. Reinfection during subsequent seasons is common. The cellular immune response to RSV infection is also important for the clearance of virus. This immune response, vital for host defense against RSV, is also implicated in the immunopathogenesis of severe lower respiratory tract RSV bronchiolitis. Many details of the immunology and immunopathologic mechanisms of RSV disease known at present have been learned from rodent models of RSV disease and are discussed in some detail. In addition, the roles of immunoglobulin E, histamine, and eosinophils in the immunopathogenesis of RSV disease are considered. Although the treatment of RSV bronchiolitis is primarily supportive, the role of ribavirin is briefly discussed. Novel approaches to the development of new antiviral drugs with promising anti-RSV activity in vitro are also described.

Respiratory syncytial virus (RSV) disease and prospects for its control

Respiratory syncytial virus (RSV) is a major virus pathogen of infants and young children, an important cause of disease in adults and is responsible for a significant amount of excess morbidity and mortality in the elderly. It also can be devastating in immunosuppressed populations. Vaccines are being developed, but none are currently licensed. Moreover, even if one or more are approved, they may not be suitable for some populations vulnerable to RSV (e.g. very young infants and the immunosuppressed). Ribavirin and immunoglobulin preparations with high titers of RSV-specific neutralizing antibodies are currently approved for use to treat and prevent RSV infection. However, neither of these is cost-effective or simple to administer. New agents are needed to reduce the impact of RSV. This review is concerned with the means currently available for controlling RSV, the search for new agents effective against this virus, and future prospects for preventing and treating RSV infections.

Approaches to antiviral chemotherapy for acute respiratory infections

The causative agents of acute respiratory infections (ARI) in infants and children are mostly thought to be viruses. Some ARI in adult patients may be caused by bacteria but most often the causes are virus infections. When ARI affect immunocompromised patients or the elderly the mortality rates are significantly higher than in immunocompetent individuals. Many types of viruses cause ARI. Among them, influenza viruses A and B and respiratory syncytial virus (RSV) are thought to be the most important because of the severity of illness after infection and their high communicability in the human population. Recently, several novel antiviral drugs against ARI have been developed and some are proceeding in clinical trials. This review covers current investigations into antiviral compounds targeted at several points in the virus life-cycle. This includes PM-523, which broadly inhibits ortho- and paramyxo-viruses, two neuraminidase inhibitors for influenza virus, neutralizing antibody to RSV and chimeric soluble ICAM-1-IgA molecules targeted against rhinoviruses.

Rehospitalization with respiratory syncytial virus after neonatal intensive care unit discharge: A 3-year follow-up

OBJECTIVES

This study sought to determine 1) the incidence of rehospitalization with respiratory syncytial virus (RSV) infection within a 3-year follow-up among infants discharged from the neonatal intensive care unit (NICU), and 2) to examine associations between age at readmission and medical and sociodemographic characteristics among infants rehospitalized with RSV.

METHODS

A 3-year retrospective review of NICU discharges at a tertiary care center identified 2506 infants. Using medical record numbers linked with International Classification of Diseases, 9th ed, diagnostic codes for RSV infection, bronchiolitis, or respiratory distress, 67 NICU graduates were identified as having been readmitted from November to April (RSV season). Bivariate analyses and logistic regression modeling were applied to determine the association between a series of predictor variables and age at readmission with RSV by 90 days, 125 days, and 180 days after discharge from the NICU.

RESULTS

The 3-year incidence of readmission with RSV infection after NICU discharge was 2.7%. During the 3-year follow-up, 6.4% of very low birth weight infants, 2.8% of low birth weight infants, and 1.7% of normal weight infants were readmitted with RSV. Crude results revealed that the presence of bacteremia, intraventricular hemorrhage, and necrotizing enterocolitis, as well as ventilation use, were associated with younger age at readmission with RSV. Simultaneous consideration of the effects of all of these medical predictors and birth weight on age at readmission revealed that normal birth weight was the only significant factor associated with younger age at readmission with RSV.

CONCLUSIONS

This study found significantly lower rates of RSV readmission among NICU graduates than those reported previously in the literature. Based on these data, prophylactic treatment of all preterm infants may not be warranted.

Prevention and treatment recommendations for respiratory syncytial virus infection. Background and clinical experience 40 years after discovery

Though 40 years have passed since its discovery, respiratory syncytial virus (RSV), one of the most ubiquitous viruses known, continues to evade most of our efforts to prevent or treat the clinical disease it causes. Long recognised as the most common cause of lower respiratory tract infections in virtually all children in the first 2 years of life, it has been increasingly recognised as a cause of more serious disease in several 'high risk' populations. These populations include infants with cardiac or pulmonary disease and infants and adults with immunodeficiencies, particularly those undergoing bone marrow transplantation. Early attempts to immunise children with a simple formalin-inactivated vaccine led to severe disease in vaccinated children who subsequently were infected with RSV from the community. Other vaccine constructs have failed for a variety of reasons, although surface glycoprotein subunit vaccines may hold promise. For years, ribavirin, a synthetic nucleoside analogue administered by constant aerosol, has been felt by many to lead to more rapid improvement in clinical disease caused by RSV, but it is still unclear whether its benefits are truly significant. An intravenous immunoglobulin product prepared from donors screened for the presence of high titres of RSV neutralising antibody (known as RSVIG) appears to be well tolerated and relatively effective in protecting high-risk infants against serious RSV disease, although therapeutic use has proven less dramatic. At least one monoclonal antibody undergoing current testing may prove easier to use in similar immunoprophylactic use. Results on the use of corticosteroids as supportive therapy have not been conclusive. In short, RSV will continue to be a challenge for clinicians and researchers well into the next century.

Community respiratory viruses in individuals with human immunodeficiency virus infection

Respiratory viruses, particularly influenza viruses, respiratory syncytial virus (RSV), parainfluenza viruses, and adenoviruses, are ubiquitous pathogens among humans, especially among young children. However, relatively little is known about the impact of these common infections on individuals with the human immunodeficiency virus (HIV). A review of the literature identifies three key areas that need further exploration. First, moderate-to-severe and even fatal lower respiratory viral illnesses in HIV-infected individuals have been reported. In general, the clinical presentation of these respiratory viral infections in persons with HIV infection is similar to their presentation in individuals without HIV infection. The major exception is the occurrence of fulminant, and often fatal, disseminated adenovirus infection in adults and children with HIV disease. Despite these reports, no information is available regarding the frequency of moderate-to-severe respiratory viral illnesses in individuals with HIV infection. Epidemiologic studies of respiratory viral illnesses in cohorts of HIV-infected adults and children are needed. Second, prolonged shedding of respiratory viruses for weeks and even months has been documented in HIV-infected adults and children. The frequency of prolonged shedding in this population has not been well defined, but data from a small newborn cohort study suggest that, at least for RSV, prolonged shedding is common. Prolonged respiratory viral shedding has implications for infection control in medical facilities where HIV-infected individuals are treated and in nursing homes, child care centers, and group foster homes that provide care for HIV-infected individuals. Therapies to help eliminate these chronic viral infections should be explored. Finally, indirect evidence suggests that respiratory viral infection may result in changes in HIV replication and, theoretically, HIV disease progression. Increased HIV-1 replication has been demonstrated in vitro in T lymphoma cells exposed to genetic material from adenovirus. Increased HIV replication in peripheral blood from adults following inactivated influenza vaccination has been reported. The impact of natural respiratory viral infection (and perhaps vaccination against these pathogens) on HIV replication and disease progression will be an important area of study.

HIV in children

Because children acquire HIV infection differently than adults, this article begins with a discussion of the epidemiology of AIDS in children. This is followed by a discussion of factors related to progression of the disease and survival in pediatric AIDS. A discussion of the pulmonary manifestations in children is followed by a suggested approach to the HIV-infected child with respiratory symptoms.

Viruses and other miscellaneous organisms

Pulmonary infections caused by several types of viruses and other miscellaneous organisms may cause disease in HIV infection. Evidence suggests that pulmonary conditions may result from infections of the lung by HIV itself. Other viruses, most commonly cytomegalovirus, may be primary perpetrators of pneumonitis or may contribute to diseases caused by coexisting infections. Although diagnosis and assessment of the clinical significance of these infections may be difficult, their recognition is of practical importance because potentially effective therapeutic agents are available for several of them. Miscellaneous infections such as pulmonary toxoplasmosis and pertussis are other uncommon but potentially treatable complications of HIV disease.

Pediatric human immunodeficiency virus infection

In the past decade, an increase in pediatric human immunodeficiency virus (HIV) infection has had a substantial impact on childhood morbidity and mortality worldwide. The vertical transmission of HIV from mother to infant accounts for the vast majority of these cases. Identification of HIV-infected pregnant women needs to be impoved so that appropriate therapy can be initiated for both mothers and infants. While recent data demonstrate a dramatic decrease in HIV transmission from a subset of women treated with zidovudine during pregnancy, further efforts at reducing transmission are desperately needed. This review focuses on vertically transmitted HIV infection in children, its epidemiology, diagnostic criteria, natural history, and clinical manifestations including infectious and noninfectious complications. An overview of the complex medical management of these children ensues, including the use of antiretroviral therapy. Opportunistic infection prophylaxis is reviewed, along with the important role of other supportive therapies.

Respiratory syncytial virus infections in pediatric renal transplant recipients

Immunocompromised patients are considered at increased risk from respiratory syncytial virus (RSV) infection. We examined the incidence and outcome of RSV infection in pediatric renal transplant (Tx) recipients on chronic immunosuppressive therapy. Of 173 recipients transplanted between November 1985 and April 1993, 5 (3%) developed RSV infection (age range 11-39 months). Initial immunosuppression included prednisone, azathioprine, cyclosporine, and polyclonal antibody therapy. Time from Tx to onset of RSV infection was 1 day to 7 months. Symptoms included rhinorrhea, cough, tachypnea, retractions, fever, wheezing, and abnormal chest X-ray. Treatment included bronchodilator therapy, bronchial drainage, ribavirin, and mist tent. Azathioprine was transiently withheld for leukopenia during treatment in 2 recipients. Three recipients developed biopsy-proven acute rejection during (n = 2) or immediately following (n = 1) RSV infection; all responded to corticosteroid treatment. RSV infection is not commonly diagnosed in pediatric renal Tx recipients. The course of RSV infection in our patients did not differ from that reported in normal children. The possible association between RSV and acute rejection warrants further observation. When diagnosed early, RSV infection does not appear to be associated with increased mortality in pediatric renal Tx recipients. Larger numbers of recipients need to be studied to confirm these results.