Twenty years of outpatient respiratory syncytial virus infection: a framework for vaccine efficacy trials

Predicted effectiveness of vaccines and extended half-life monoclonal antibodies against RSV hospitalizations in children

Several vaccines and extended half-life monoclonal antibodies (mAbs) against respiratory syncytial virus (RSV) have shown promise in clinical trials. We used age-structured transmission models to predict the possible impact of various RSV prevention strategies including maternal immunization, live-attenuated vaccines, and long-lasting mAbs. Our results suggest that maternal immunization and long-lasting mAbs are likely to be highly effective in preventing RSV hospitalizations in infants under 6 months of age, averting more than half of RSV hospitalizations in neonates. Live-attenuated vaccines could reduce RSV hospitalizations in vaccinated age groups and are also predicted to have a modest effect in unvaccinated age groups because of disruptions to transmission. Compared to year-round vaccination, a seasonal vaccination program at the country level provides at most a minor advantage regarding efficiency. Our findings highlight the substantial public health impact that upcoming RSV prevention strategies may provide.

OUP accepted manuscript

Background

Limited data are available on the economic costs of respiratory syncytial virus (RSV) infections among infants and young children in the United States.

Methods

We performed a systematic literature review of 10 key databases to identify studies published between 1 January 2014 and 2 August 2021 that reported RSV-related costs in US children aged 0–59 months. Costs were extracted and a systematic analysis was performed.

Results

Seventeen studies were included. Although an RSV hospitalization (RSVH) of an extremely premature infant costs 5.6 times that of a full-term infant ($10 214), full-term infants accounted for 82% of RSVHs and 70% of RSVH costs. Medicaid-insured infants were 91% more likely than commercially insured infants to be hospitalized for RSV treatment in their first year of life. Medicaid financed 61% of infant RSVHs. Paying 32% less per hospitalization than commercial insurance, Medicaid paid 51% of infant RSVH costs. Infants’ RSV treatment costs $709.6 million annually, representing $187 per overall birth and $227 per publicly funded birth.

Conclusions

Public sources pay for more than half of infants’ RSV medical costs, constituting the highest rate of RSVHs and the highest expenditure per birth. Full-term infants are the predominant source of infant RSVHs and costs.

Number needed to immunize to prevent RSV with extended half-life monoclonal antibody

BACKGROUND

Respiratory syncytial virus (RSV) is one of the most important respiratory pathogens in young children. Infants <6 months of age and infants and young children with extreme pre-term birth, and cardiac and pulmonary co-morbidities experience the highest incidence of severe RSV disease. There are no licensed vaccines; immunoprophylaxis is recommended for the highest risk children. Extended half-life RSV monoclonal antibodies (EHL-mAbs) are under development intended for immunization of all infants and high-risk children <2 years of age. We modeled the anticipated public health benefits of RSV EHL-mAb immunization using the number needed to immunize (NNI).

METHODS

We combined RSV hospitalization, outpatient and outpatient lower respiratory tract infection (LRI) incidence estimates and a range of immunization efficacies to estimate the annual NNI. We calculated the absolute incidence rate reduction (ARR) by multiplying the incidence rates by immunization efficacy. NNI was calculated as the reciprocal of the ARR.

RESULTS

For an RSV EHL-mAb with 70% efficacy, 6-18 infants would need to be immunized to prevent one RSV-associated outpatient visit, and 13-33 infants would need to be immunized to prevent one RSV-associated LRI outpatient visit. To prevent one RSV-associated hospitalization, 37-85 infants 0-5 months of age, and 107-280 infants 6-11 months of age would need to be immunized.

CONCLUSIONS

Public health benefits, such as disease cases averted due to immunization, are essential elements in consideration of candidate vaccines for a national immunization program. An RSV EHL-mAb of moderate efficacy could have high impact. These data provide an additional perspective for public health decision making.

Viral Inhibition of the IFN-Induced JAK/STAT Signalling Pathway: Development of Live Attenuated Vaccines by Mutation of Viral-Encoded IFN-Antagonists

The interferon (IFN) induced anti-viral response is amongst the earliest and most potent of the innate responses to fight viral infection. The induction of the Janus kinase/signal transducer and activation of transcription (JAK/STAT) signalling pathway by IFNs leads to the upregulation of hundreds of interferon stimulated genes (ISGs) for which, many have the ability to rapidly kill viruses within infected cells. During the long course of evolution, viruses have evolved an extraordinary range of strategies to counteract the host immune responses in particular by targeting the JAK/STAT signalling pathway. Understanding how the IFN system is inhibited has provided critical insights into viral virulence and pathogenesis. Moreover, identification of factors encoded by viruses that modulate the JAK/STAT pathway has opened up opportunities to create new anti-viral drugs and rationally attenuated new generation vaccines, particularly for RNA viruses, by reverse genetics.

Challenges and opportunities in developing respiratory syncytial virus therapeutics

Two meetings, one sponsored by the Wellcome Trust in 2012 and the other by the Global Virology Foundation in 2013, assembled academic, public health and pharmaceutical industry experts to assess the challenges and opportunities for developing antivirals for the treatment of respiratory syncytial virus (RSV) infections. The practicalities of clinical trials and establishing reliable outcome measures in different target groups were discussed in the context of the regulatory pathways that could accelerate the translation of promising compounds into licensed agents. RSV drug development is hampered by the perceptions of a relatively small and fragmented market that may discourage major pharmaceutical company investment. Conversely, the public health need is far too large for RSV to be designated an orphan or neglected disease. Recent advances in understanding RSV epidemiology, improved point-of-care diagnostics, and identification of candidate antiviral drugs argue that the major obstacles to drug development can and will be overcome. Further progress will depend on studies of disease pathogenesis and knowledge provided from controlled clinical trials of these new therapeutic agents. The use of combinations of inhibitors that have different mechanisms of action may be necessary to increase antiviral potency and reduce the risk of resistance emergence.

Single, dual and multiple respiratory virus infections and risk of hospitalization and mortality

Respiratory virus infections cause a significant number of hospitalization and deaths globally. This study investigated the association between single and multiple respiratory virus infections and risk of admission to a general ward, intensive care unit or death in patients aged 0-105 years (mean ± s.d. = 24·4 ± 24·1 years), from North West England, that were tested for respiratory virus infections between January 2007 and June 2012. The majority of infections were in children aged ⩽5 years. Dual or multiple infections occurred in 10·4% (1214/11 715) of patients, whereas single infection occurred in 89·6% (10 501/11 715). Rhinovirus was the most common co-infecting virus (occurring in 69·5%; 844/1214 of co-infections). In a multivariate logistic regression model, multiple infections were associated with an increased risk of admission to a general ward [odds ratio (OR) 1·43, 95% confidence interval (CI) 1·2-1·7, P < 0·0001]. On the other hand, patients with respiratory syncytial virus (RSV) and human parainfluenza virus types 1-3 (hPIV1-3), as a single infection, had a higher risk of being admitted to a general ward (OR 1·49, 95% CI 1·28-1·73, P < 0·0001 and OR 1·34, 95% CI 1·003-1·8, P = 0·05, respectively); admitted to an intensive-care unit or dying (OR 1·5, 95% CI 1·20-2·0, P = 0·001 and OR 1·60, 95% CI 1·02-2·40, P = 0·04, respectively). This result emphasizes the importance of RSV, hPIV and mixed infections and calls for research on vaccines, drugs and diagnostic tests targeting these respiratory viruses.

Human Respiratory Viruses☆

Viruses are the leading causes of acute lower respiratory-tract infection in infancy. Respiratory syncytial virus (RSV) is the most common pathogen in severe disease, with hMPV, PIV-3, influenza viruses, and rhinoviruses accounting for the majority of the remainder of acute viral respiratory infections. Humans generally do not develop lifelong immunity to reinfection with these viruses; rather, specific immunity protects against severe and lower respiratory-tract disease.

The incidence and clinical burden of respiratory syncytial virus disease identified through hospital outpatient presentations in Kenyan children

Background

There is little information that describe the burden of respiratory syncytial virus (RSV) associated disease in the tropical African outpatient setting.

Methods

We studied a systematic sample of children aged <5 years presenting to a rural district hospital in Kenya with acute respiratory infection (ARI) between May 2002 and April 2004. We collected clinical data and screened nasal wash samples for RSV antigen by immunofluorescence. We used a linked demographic surveillance system to estimate disease incidence.

Results

Among 2143 children tested, 166 (8%) were RSV positive (6% among children with upper respiratory tract infection and 12% among children with lower respiratory tract infection (LRTI). RSV was more likely in LRTI than URTI (p<0.001). 51% of RSV cases were aged 1 year or over. RSV cases represented 3.4% of hospital outpatient presentations. Relative to RSV negative cases, RSV positive cases were more likely to have crackles (RR = 1.63; 95% CI 1.34–1.97), nasal flaring (RR = 2.66; 95% CI 1.40–5.04), in-drawing (RR = 2.24; 95% CI 1.47–3.40), fast breathing for age (RR = 1.34; 95% CI 1.03–1.75) and fever (RR = 1.54; 95% CI 1.33–1.80). The estimated incidence of RSV-ARI and RSV-LRTI, per 100,000 child years, among those aged <5 years was 767 and 283, respectively.

Conclusion

The burden of childhood RSV-associated URTI and LRTI presenting to outpatients in this setting is considerable. The clinical features of cases associated with an RSV infection were more severe than cases without an RSV diagnosis.

Influenza and respiratory syncytial virus (RSV) vaccines for infants: safety, immunogenicity, and efficacy

Respiratory viral infections in infants and young children frequently cause illness that can easily progress to hospitalization and death. There are currently no licensed vaccines to prevent respiratory viral disease in children younger than 6 months, reflecting safety concerns and the difficulty in inducing effective immune responses in infants. This review discusses vaccines that have been developed, or are currently being developed, against influenza and respiratory syncytial virus, with a focus on studies performed to demonstrate their safety and efficacy, and the impact of immunologic immaturity and maternal antibodies on the infant response to vaccines.

Clinical characteristics of respiratory syncytial virus infection in neonates and young infants

INTRODUCTION/AIM

Infection with respiratory syncytial virus (RSV) occurs during the first year of life in 50% of children and 20%-40% of them have signs of lower respiratory tract infection (bronchiolitis or pneumonia). There is an increased risk for complicated course and death from RSV infection in premature infants, especially those with bronchopulmonary dysplasia (BPD) or congenital heart disease. The aim of our study was to analyze clinical characteristics of laboratory confirmed RSV infection in order to evaluate the need for preventive measures in neonates and young infants.

METHODS

The prospective study included children under age of 12 months admitted to our hospital in the period November 2008-March 2009 who were positive for RSV by enzyme immunoassay membrane test. The course of disease was assessed by clinical score and radiographic findings.

RESULTS

Infection with RSV was confirmed in 91 patients: 21 (23.0%) were under the age of 30 days, 37 (40.7%) were between 31-60 days, and 33 patients (36.3%) were older than 60 days (p > 0.05). The highest hospitalization rate was in January--33 patients (36.3%; p < 0.01). Disease severity score in these age groups (AG) were: 8.4 +/- 0.4 (AG 0-30 days); 9.0 +/- 0.3 (AG 31-60 days) and 8.3 +/- 0.3 (AG > 60 days), without statistically significant difference among the groups (p > 0.05). Clinical scores in patients with and without risk factors were 10.5 +/- 0.5 and 8.3 +/- 0.2, respectively (p < 0.01). Pathological radiographic findings were observed in 72 (79.1%) and complications (apnea, significant atelectasis, encephalopathy) occured in 15 (16.5%) patients. The average length of hospital stay in complicated and uncomplicated course of the disease was 9 days and 6 days, respectively (p < 0.01). Therapy in 85 (93.4%) patients included bronchodilators, while systemic glucocorticoids and oxygen therapy were used in 51 (56.0%) and 44 (48.4%) patients, respectively. Death occured in 2 (2.2%) patients, both from a high risk group (the patient with BPD and the other one with congenital heart disease and Down syndrome).

CONCLUSION

Infection with RSV in our settings showed marked seasonal characteristics with highest hospitalization rate in January. Although the course and outcome of the disease were favorable in the majority of our patients, the need for hospitalization and administration of therapy with possible side effects warrants that general measures for prevention of respiratory infections are followed especially in the first year of life. Severe disease and death are more probable in neonates and infants with risk factors. In these children passive immunisation with specific monoclonal antibody (e.g. palivizumab) during RSV season should be considered.

Etiology and epidemiology of viral pneumonia among hospitalized children in rural Mozambique: a malaria endemic area with high prevalence of human immunodeficiency virus

BACKGROUND

The role of viruses in pediatric pneumonia remains poorly studied in sub-Saharan Africa, where pneumonia-associated mortality is high.

METHODS

During a 1-year hospital-based surveillance, a nasopharyngeal aspirate (NPA) was collected from children aged <5 years admitted to hospital in rural Mozambique with clinically severe pneumonia. Identification of 12 respiratory viruses was performed by polymerase chain reactions (PCR). Study children were also tested for invasive bacterial infection (IBI), Plasmodium falciparum parasitemia, and HIV.

RESULTS

Almost half (394/807) of the children hospitalized with clinically severe pneumonia had at least one respiratory virus detected. A total of 475 viruses were detected among these 394 children, the most prevalent ones were rhinovirus (41%), adenovirus (21%), and respiratory syncytial virus (11%). Eleven percent of viral infected children had concomitant IBI, 15% had malaria parasites, and 25% had HIV coinfection. Viral infection was 5.5 to 16 times more prevalent among HIV-infected children and incidence rate ratios varied according to virus. Inhospital mortality of viral cases was 9%, being highest among cases with IBI coinfection (odds ratio = 7) or HIV infection (odds ratio = 7).

CONCLUSIONS

Study results highlight the high prevalence of respiratory viruses among hospitalized pneumonia cases in Mozambique. HIV infection is an important contributor to the high burden of disease and associated mortality of viral pneumonia. IBI also contributes to a worse prognosis of viral cases. Strategies to prevent mother-to-child transmission of HIV as well as introduction of Hib and pneumococcal vaccines could have a substantial impact on reduction of viral pneumonia and associated mortality among children in rural Africa.

LDH concentration in nasal-wash fluid as a biochemical predictor of bronchiolitis severity

OBJECTIVE

Because the decision to hospitalize an infant with bronchiolitis is often supported by subjective criteria and objective indicators of bronchiolitis severity are lacking, we tested the hypothesis that lactate dehydrogenase (LDH), which is released from injured cells, is a useful biochemical indicator of bronchiolitis severity.

PATIENTS AND METHODS

We retrospectively analyzed a study of children <24 months old presenting to the emergency department with bronchiolitis. Demographic, clinical information, nasal wash (NW), and serum specimens were obtained. NW samples were analyzed for respiratory viruses, caspase 3/7 activity, and a panel of cytokines and chemokines. Total LDH activity was tested in NW samples and sera.

RESULTS

Of 101 enrolled children (median age: 5.6 months), 98 had NW specimens available. A viral etiology was found for 82 patients (83.6%), with respiratory syncytial virus (RSV) (66%) and rhinovirus (19%) being the most common viruses detected. Concentrations of LDH in NW specimens were independent from those in sera and were higher in children with RSV infection or with dual infection. Significant correlations were found between NW LDH and NW cytokines/chemokines. Similarly, NW LDH correlated with NW-caspase 3/7 activity (r = 0.75; P < .001). In a multivariate analysis, NW LDH concentration in the upper quartile was significantly associated with a reduced risk of hospitalization (odds ratio: 0.19 [95% confidence interval: 0.05-0.68]; P = .011).

CONCLUSIONS

NW LDH levels in young children with bronchiolitis varied according to viral etiology and disease severity. Values in the upper quartile were associated with approximately 80% risk reduction in hospitalization, likely reflecting a robust antiviral response. NW LDH may be a useful biomarker to assist the clinician in the decision to hospitalize a child with bronchiolitis.

Clinical presentation and severity of viral community-acquired pneumonia in young Nepalese children

BACKGROUND

Most deaths from pneumonia in children <5 years of age occur in developing countries, where information about the clinical impact and severity of viral causes of respiratory infections is limited.

METHODS

From June 29, 2004 to June 30, 2007 we evaluated 2230 cases of pneumonia (World Health Organization criteria) in children aged 2 to 35 months in Bhaktapur, Nepal. A nasopharyngeal aspirate from each case was examined for 7 respiratory viruses using reverse-transcription polymerase chain reaction. We compared illness duration, severity, and treatment failure between cases positive and negative for the individual viruses in multiple regression models.

RESULTS

A total of 2219 cases had a valid polymerase chain reaction result and were included in the analyses. Overall, 46.1% of cases were 2 to 11 months of age. Being infected with respiratory syncytial virus (RSV) was associated with lower chest indrawing (odds ratio [OR] 2.17; 95% confidence interval [CI] 1.42-3.30) and, among infants, oxygen saturation <93% (OR: 1.88; CI: 1.32-2.69). Among the 2088 nonsevere pneumonia cases, those positive for RSV had a longer time to recovery (hazard ratio 0.82; CI 0.75-0.90; P < 0.001) and an increased risk of treatment failure (OR: 1.75; CI: 1.34-2.28; P < 0.001) than the RSV negative cases.

CONCLUSIONS

Being infected with RSV was associated with a more severe clinical presentation of pneumonia, longer illness duration, and increased risk of treatment failure. The severity of RSV infection was age related, infants being more severely affected.

Breastfeeding reduces the severity of respiratory syncytial virus infection among young infants: a multi-center prospective study

BACKGROUND

The objective of this study was to evaluate the effects of breastfeeding on the severity of respiratory syncytial virus infection in early infancy.

METHODS

A rapid test for respiratory syncytial virus (RSV) was administered by 16 general pediatricians from May 2002 to April 2005 in infants undergoing medical checkups for the common cold, all of whom were 100 days old or younger and had birthweights of more than 2500 g without underlying disease. Infants were divided into three groups: the Full breastfeeding group, the Partial group, and the Token group. RSV-positive cases were followed up for 10 days after the initial diagnosis and the following three points were investigated: (i) the incidence of hospitalization; (ii) the duration of hospitalization; and (iii) the incidence of requiring oxygen therapy.

RESULTS

RSV antigen was detected in 203 of the total of 892 cases, and these were diagnosed as cases of RSV infectious disease. Although there were no significant differences in the hospitalization rate among the three groups, there were significant differences in the duration of hospitalization and the rate of requiring oxygen therapy. Multivariate logistic regression revealed that the requirement of oxygen therapy was significantly lower in the Full breastfeeding group (P= 0.032; odds ratio, 0.256; 95% confidence interval, 0.074-0.892).

CONCLUSIONS

Breastfeeding reduces the severity of respiratory syncytial virus infection in early infancy.

The pediatric burden of human coronaviruses evaluated for twenty years

BACKGROUND

The epidemiology of human coronaviruses (HCoVs) has not been established using reverse transcription polymerase chain reaction techniques in a specimen collection that spans decades.

METHODS

We used real-time RT-PCR for 3 HCoVs, HCoV 229E, OC43, and NL63, to test nasal wash specimens that had been obtained from a cohort of children <5 years of age with upper or lower respiratory infection (URI, LRI) who were comprehensively followed during the period from 1977 to 2001. Prospectively collected clinical data and archival samples were analyzed.

RESULTS

HCoV was detected in 92/1854 (5.0%) of available samples with no known viral etiology of which 9% were 229E, 59% OC43, and 33% NL63. This represented 10/119 (8.4%) of LRI samples and 82/1735 (4.7%) of URI samples. HCoV was not detected every year, but occurred episodically. The recently described HCoV-NL63 was detected as early as 1981. HCoV was associated with 11.4 LRI episodes/1000 child-years <5 years of age (all in children <2 years of age) and 67.3 URI episodes/1000 child-years <5 years of age.

CONCLUSIONS

HCoV-NL63 and OC43 are associated with a significant proportion of LRI in children less than 2 years of age and a substantial number of medically attended URI episodes.

Respiratory syncytial virus infection and disease in infants and young children observed from birth in Kilifi District, Kenya

BACKGROUND

In developing countries, there are few data that characterize the disease burden attributable to respiratory syncytial virus (RSV) and clearly define which age group to target for vaccine intervention.

METHODS

Six hundred thirty-five children, recruited during the period 2002-2003, were intensively monitored until each experienced 3 epidemics of RSV infection. RSV infection was diagnosed using immunofluorescence of nasal washing specimens collected at each episode of acute respiratory infection. Incidence estimates were adjusted for seasonality of RSV exposure.

RESULTS

For 1187 child-years of observation (CYO), a total of 409 (365 primary and 82 repeat) episodes of RSV infection were identified. Adjusted incidence estimates of lower respiratory tract infection (LRTI), severe LRTI, and hospital admission were 90 cases per 1000 CYO, 43 cases per 1000 CYO, and 10 cases per 1000 CYO, respectively, and corresponding estimates among infants were 104 cases per 1000 CYO, 66 cases per 1000 CYO, and 13 cases per 1000 CYO, respectively. The proportion of cases of all-cause LRTI, and severe LRTI and hospitalizations attributable to RSV in the cohort was 13%, 19%, and 5%, respectively. Fifty-five percent to 65% of RSV-associated LRTI and severe LRTI occurred in children aged >6 months. The risk of RSV disease following primary symptomatic infection remained significant beyond the first year of life, and one-quarter of all reinfections were associated with LRTI.

CONCLUSIONS

RSV accounts for a substantial proportion of the total respiratory disease in this rural population; we estimate that 85,000 cases of severe LRTI per year occur in infants in Kenya. The majority of this morbidity occurs during late infancy and early childhood--ages at which the risk of disease following infection remains significant. Disease resulting from reinfection is common. Our results inform the debate on the target age group and effectiveness of a vaccine.

The absence of enhanced disease with wild type respiratory syncytial virus infection occurring after receipt of live, attenuated, respiratory syncytial virus vaccines

Early in the development of respiratory syncytial virus (RSV) vaccines severe disease occurred in children after receipt of formalin-inactivated RSV vaccine. Continuing efforts to develop an appropriately attenuated and immunogenic live RSV vaccine have given opportunities to assure that live vaccines are safe through surveillance of children after vaccination. In the present study, the rate of RSV-associated upper respiratory tract illness in 388 children was lower in RSV vaccinated children than in controls (14% versus 20% in a 6-24 month old group and 16% versus 25% in infants). Additionally, there was no evidence that vaccination predisposed to more severe lower respiratory tract illness. Thus infection with a series of live attenuated RSV vaccines did not result in enhanced disease upon infection with wild type RSV. The impact of RSV during this surveillance will inform the design of future efficacy studies with RSV vaccines.

Comparison of electronic microarray to enzyme hybridization assay for multiplex reverse-transcriptase PCR detection of common respiratory viruses in children

A new assay, composed of the NGEN RVA (Nanogen, Inc., San Diego, CA; Prodesse, Inc., Waukesha, WI), which is a pair of analyte-specific reagents that allow the multiplex reverse transcriptase polymerase chain reaction (RT-PCR) and electronic microarray detection of influenza virus A and B, respiratory syncytial virus A and B, and human parainfluenza virus types 1, 2, and 3, was evaluated in comparison with the Hexaplex (Prodesse), a multiplex RT-PCR–enzyme hybridization assay. Comparisons included the detection of respiratory viruses from whole-virus stocks (ATCC) and from frozen pediatric respiratory specimens collected at Children's Hospital of Wisconsin between 1991 and October 1998. After the retesting of six indeterminants and 20 discrepants, overall agreement improved to 96% on the positives and 100% on negatives, with only eight specimens still discrepant. The RVA reagents allow a rapid, sensitive, and specific assay for detecting seven of the most common respiratory viruses in children.

Role of respiratory syncytial virus in acute otitis media: implications for vaccine development

We summarize herein the results of various virologic studies of acute otitis media (AOM) conducted at our site over a 10-year period. Among 566 children with AOM, respiratory syncytial virus (RSV) was the most common virus identified in either middle ear fluid or nasal wash; it was found in 16% of all children and 38% of virus-positive children. Seventy-one percent of the children with RSV were 1 year of age or older, which was significantly older than all other viruses combined (P=0.045). RSV infection was associated with the common bacterial pathogens causing AOM. Past efforts to develop vaccines for RSV have emphasized prevention of lower respiratory tract infection in infants, which is a more serious problem but less common than AOM. Our results suggest that RSV vaccines that work only against infection in older children may have value in preventing AOM, the most common pediatric disease.

The histopathology of fatal untreated human respiratory syncytial virus infection

The pathology of respiratory syncytial virus (RSV) infection was evaluated 1 day after an outpatient diagnosis of RSV in a child who died in a motor vehicle accident. We then identified 11 children with bronchiolitis from the Vanderbilt University autopsy log between 1925 and 1959 who met criteria for possible RSV infection in the preintensivist era. Their tissue was re-embedded and evaluated by routine hematoxylin and eosin and PAS staining and immunostaining with RSV-specific antibodies. Tissue from three cases was immunostain-positive for RSV antigen and was examined in detail. Small bronchiole epithelium was circumferentially infected, but basal cells were spared. Both type 1 and 2 alveolar pneumocytes were also infected. Although, not possible for archival cases, tissue from the index case was evaluated by immunostaining with antibodies to define the cellular components of the inflammatory response. Inflammatory infiltrates were centered on bronchial and pulmonary arterioles and consisted of primarily CD69+ monocytes, CD3+ double-negative T cells, CD8+ T cells, and neutrophils. The neutrophil distribution was predominantly between arterioles and airways, while the mononuclear cell distribution was in both airways and lung parenchyma. Most inflammatory cells were concentrated submuscular to the airway, but many cells traversed the smooth muscle into the airway epithelium and lumen. Airway obstruction was a prominent feature in all cases attributed to epithelial and inflammatory cell debris mixed with fibrin, mucus, and edema, and compounded by compression from hyperplastic lymphoid follicles. These findings inform our understanding of RSV pathogenesis and may facilitate the development of new approaches for prevention and treatment.

Influenza related hospitalisations in Sydney, New South Wales, Australia

BACKGROUND

Routine influenza vaccination for children aged 6-23 months has recently been recommended in the United States. Accurate assessment of influenza related burden of illness in children could support similar recommendations in other settings. However, routinely available data underestimate the role of influenza in causing hospitalisation, and indirect estimation methods face difficulties controlling for the concurrent circulation of respiratory syncytial virus (RSV). Recent studies from Hong Kong and the United States have used differing methods to estimate the true burden of influenza related hospitalisation, with disparate results.

METHODS

Retrospective population based study of children less than 18 years of age from Sydney, Australia, 1994 to 2001. Using two previously reported methods, estimates of annual hospitalisation rates attributable to influenza were derived by comparison of mean hospitalisation rates for acute respiratory disease during periods of high influenza activity and low RSV activity (defined using virological surveillance data) and periods where both influenza and RSV activity were low. These estimates were compared to rates of hospitalisation where influenza was recorded as the principal discharge diagnosis.

RESULTS

Hospitalisation rates attributable to influenza were up to 11 times higher, depending on the age group and method used, compared to rates calculated from principal discharge diagnosis codes.

CONCLUSIONS

Although there remains considerable uncertainty in estimating influenza related morbidity by methods using excess hospitalisations, even minimum estimates of disease burden warrant consideration of routine influenza immunisation for all children less than 2 years of age. Such estimates, derived from principal discharge diagnosis codes, are available in most settings.

The role of human metapneumovirus in upper respiratory tract infections in children: a 20-year experience

BACKGROUND

The role that human metapneumovirus (hMPV) plays in the etiology of upper respiratory tract infections (URIs) in children over a period of many years has not been evaluated previously.

METHODS

By use of real-time reverse-transcriptase polymerase chain reaction, we retrospectively tested nasal wash (NW) specimens for hMPV that had been obtained from a cohort of 1532 infants and children with URIs who were prospectively followed for an average of 2.4 years during the period from 1982 to 2001. Virus genes were sequenced, and prospectively collected clinical data were analyzed.

RESULTS

There were 2710 visits for URIs for which routine cultures did not reveal a viral etiology. Archival NW specimens from 2384 of these visits were available. hMPV RNA was detected in 118 (5%) of 2384 specimens. The mean age of the children with hMPV infection was 20 months, and 78% of illnesses occurred from December through May. Acute otitis media (AOM) was detected in 50% of these children. hMPV circulated each year, but the numbers of isolates detected varied by year. Reinfections with both homologous and heterologous strains occurred. Four distinct genetic lineages were present over the 20 years of surveillance, with several different lineages circulating during some seasons.

CONCLUSIONS

hMPV was detected in a substantial number of children with URIs and concomitant AOM.

Seasonality of invasive pneumococcal disease: temporal relation to documented influenza and respiratory syncytial viral circulation

BACKGROUND

Seasonal fluctuation in the incidence of invasive pneumococcal disease has been attributed to winter virus exposure (e.g., influenza and respiratory syncytial virus [RSV]). Evidence of a direct correlation of invasive pneumococcal disease with laboratory-confirmed virus seasons, however, is limited. Using two prospective surveillance networks, the temporal relation between invasive pneumococcal disease and isolation of circulating winter viruses was explored.

METHODS

Episodes of invasive pneumococcal disease in five Tennessee counties were collected prospectively from January 1995 through June 2002. Virus seasons were defined using prospective laboratory-based surveillance. Correlation between weekly identification of invasive pneumococcal disease and laboratory isolation of RSV and influenza, as well as comparisons of the frequencies of invasive pneumococcal disease episodes during viral and nonviral seasons were determined.

RESULTS

A total of 4147 invasive pneumococcal disease episodes were identified. Weekly frequency of invasive pneumococcal disease correlated directly with the weekly frequency of isolation of RSV (r = 0.56, P <0.001) and influenza (r= 0.40, P <0.001). The average weekly frequency of invasive pneumococcal disease during RSV and influenza seasons was higher than during the nonviral seasons (P <0.001 for each year).

CONCLUSION

Weekly episodes of invasive pneumococcal disease correlated temporally with laboratory-confirmed weekly isolation of RSV and influenza, and the incidence of invasive pneumococcal disease was increased when these viruses were circulating in the community.

Respiratory illness during winter: a cohort study of urban children from temperate Australia

OBJECTIVE

To examine the epidemiology and burden of respiratory illness during winter in urban children from temperate Australia.

METHODS

We conducted a cohort study of healthy Melbourne children, aged from 12 to 71 months. Parents kept a daily respiratory symptom diary and recorded resource use when an influenza-like illness (ILI) occurred.

RESULTS

One-hundred and eighteen children had 137 ILI episodes over 12 weeks for a rate of 0.53 ILI episodes per child-month (95% CI 0.44-0.61). Risk factors for ILI included younger age, fewer people residing in the household, structured exposure to other children outside the home, and a higher household income. Episodes had a mean duration of 10.4 days with 64 visits to a general practitioner (46.7 GP visits per 100 episodes), 27 antibiotic courses prescribed (19.7 antibiotic courses per 100 episodes), and three overnight hospitalizations (2.2 admissions per 100 episodes). Parents reported an average of 11.7 h excess time spent caring for a child per episode.

CONCLUSIONS

Respiratory illnesses are a common and largely neglected cause of illness in Australian children. Pathogen-specific data are required to better assess the likely impact of available and developing vaccines and other treatment options.

Cost-effective use of rapid diagnostic techniques in the treatment and prevention of viral respiratory infections

The most cost-effective current use of rapid respiratory virus diagnostics is through highly sensitive and specific molecular assays (mostly PCR-based) in the hospital setting or for chronically ill or immunocompromised outpatients. Specifically, this cost savings is the result of preventing hospitalization or decreasing length of hospitalization, decreasing unnecessary testing and procedures, directing specific therapy, and reducing unnecessary antibiotic use. Equally important is community surveillance by informing physicians rapidly what agents are in the community. Important ongoing issues regarding the cost-effective use of these assays include the cost of reagents or machinery, reimbursement for testing, the need for reliable commercial reagents, the need for open platforms that can respond to new "emerging" or "reemerging" agents, and the need for proficiency panels to share between laboratories. Rapid molecular diagnostic assays for the detection of respiratory viruses have moved into the mainstream of clinical testing. These assays already play important roles in select populations and clinical situations for critical patient management. In addition, there are numerous clinical scenarios where the use of these assays should have a positive cost/benefit ratio. Further work needs to be done to demonstrate this benefit to society. Further development of multiplex assays and decreasing the cost of testing will help improve the benefit of these assays to clinical care. Work is underway on large multiplex molecular assays with high sensitivity and specificity that will be able to be used in an outpatient setting both because of speed and low cost. The future holds great potential for physicians. who soon may be able to answer the age-old question, "Doc, what do I have?" with more than, "You probably have a virus."

Effect of zinc salts on respiratory syncytial virus replication

Zinc supplementation decreases the morbidity of lower respiratory tract infection in pediatric patients in the developing world. We sought to determine if zinc mediates a specific inhibitory effect against the major cause of pediatric lower respiratory tract disease, respiratory syncytial virus (RSV). We determined the in vitro inhibitory effect of three zinc salts (zinc acetate, lactate, and sulfate) on the replication of RSV at various concentrations of 10 and 1 mM and 100 and 10 microM. The degree of inhibition of RSV replication was examined in the presence of zinc during preincubation, adsorption, or penetration and was compared with that caused by salts of other divalent cations. Complete inhibition of RSV plaque formation was observed at 1 and 10 mM, representing reductions that were >or=10(6)-fold. At the lowest concentration tested, 10 microM, we observed >or=1000-fold reductions in RSV yield when zinc was present during preincubation, adsorption, penetration, or egress of virus. The therapeutic indices, determined as ratios of 50% toxicity concentration to 50% inhibitory concentration, were 100, 150, and 120 for zinc acetate, zinc lactate, and zinc sulfate, respectively. The inhibitory effect of zinc salts on RSV was concentration dependent and was not observed with other salts containing divalent cations such as calcium, magnesium, and manganese. RSV plaque formation was prevented by pretreatment of HEp-2 cell monolayer cultures with zinc or by addition of zinc to methylcellulose overlay media after infection. The results of this study suggest that zinc mediates antiviral activity on RSV by altering the ability of the cell to support RSV replication.

Opportunities for early therapy of respiratory syncytial virus (RSV) infection: what happens before hospitalization

RSV loads of infants are already declining near the time of hospitalization. For optimal effect, antiviral and other RSV therapeutics therefore may need to be applied before this occurs. 134 RSV-hospitalized infants were studied to determine the timing of events and their healthcare seeking behavior prior to hospitalization. Sixty-two percent of infants had contact with a health care professional > or = 1 day prior to hospitalization and 46% had such a contact on > or = 2 different days prior to hospitalization. The mean (S.D.) duration of RSV symptoms prior to hospitalization was 3.9 +/- 2.3 days and prior to first health care contact was 2.6 +/- 1.8 days. RSV-hospitalized infants routinely have contact with health care professionals at significantly early time points in their illness. These contacts are potential opportunities for initiation of early anti-RSV therapy.

Failure of inactivated influenza A vaccine to protect healthy children aged 6-24 months

BACKGROUND

The efficacy of inactivated influenza vaccine in healthy infants and children younger than 24 months has not been confirmed. The aim of the present study was to determine the prophylactic effect of inactivated influenza vaccine against influenza A in healthy children aged 6-24 months.

METHODS

Healthy infants and young children (6-24 months old) were immunized by subcutaneous injection of inactivated influenza vaccine before influenza seasons. Age matched children were randomly assigned as the control. These children were followed up from January to April in each year (2000, 2001 and 2002). The attack rates of influenza A infection was compared and statistically assessed.

RESULTS

The attack rate of influenza A virus infection in the vaccine group and the control group were 14.8% (n = 27) vs 12.5% (n = 32) in 2000 (P = 0.526); 2.8% (n = 72) vs 7.2% (n = 69) in 2001 (P = 0.203); and 3.4% (n = 52) vs 8.9% (n = 56) in 2002 (P = 0.205). The attack rates of influenza A between the two groups were not significantly different.

CONCLUSIONS

Inactivated influenza vaccine did not reduce the attack rate of influenza A infection in 6-24 month old children.

Maternal morbidity and perinatal outcomes among pregnant women with respiratory hospitalizations during influenza season

OBJECTIVES

A population-based assessment of maternal and perinatal morbidity related to respiratory illness during influenza season among pregnant women has not been published. The objectives of this investigation were to describe and quantify the impact of respiratory hospitalization during pregnancy on serious maternal and perinatal morbidity.

STUDY DESIGN

A matched cohort study using an administrative database of pregnant women enrolled in the Tennessee Medicaid population to determine pregnancy outcomes associated with respiratory hospitalizations during influenza season. Pregnant women aged 15 to 44 years with a respiratory hospitalization during influenza seasons 1985-1993 were matched by gestational age and presence of comorbidity with pregnant control subjects without a respiratory hospitalization.

RESULTS

During the eight influenza seasons studied, 293 women with singleton pregnancies had respiratory disease hospitalizations (5.1:1000). Women with asthma had high rates of such hospitalization (59.7:1000). Compared with matched controls, women with respiratory hospitalizations had similar modes of delivery, delivery length of stay, and episodes of preterm labor. The prevalence of prematurity and low birth weight among infants born to such women was likewise similar between the two groups.

CONCLUSION

In this population of pregnant women, those with asthma accounted for half of all respiratory-related hospitalizations during influenza seasons, with 6% of pregnant women with asthma requiring respiratory hospitalization during influenza season, (odds ratio 10.63, 95% CI, 8.18-13.83, compared with women without a medical comorbidity). We detected no significant increase in adverse perinatal outcomes associated with respiratory hospitalizations during influenza season.

Human metapneumovirus and lower respiratory tract disease in otherwise healthy infants and children

BACKGROUND

We sought to determine the role of human metapneumovirus in lower respiratory tract illness in previously healthy infants and children.

METHODS

We tested nasal-wash specimens, obtained over a 25-year period from otherwise healthy children presenting with acute respiratory tract illness, for human metapneumovirus.

RESULTS

A viral cause other than human metapneumovirus was determined for 279 of 687 visits for acute lower respiratory tract illness (41 percent) by 463 children in a population of 2009 infants and children prospectively seen from 1976 to 2001. There were 408 visits for lower respiratory tract illness by 321 children for which no cause was identified. Of these 321 children, specimens from 248 were available. Forty-nine of these 248 specimens (20 percent) contained human metapneumovirus RNA or viable virus. Thus, 20 percent of all previously virus-negative lower respiratory tract illnesses were attributable to human metapneumovirus, which means that 12 percent of all lower respiratory tract illnesses in this cohort were most likely due to this virus. The mean age of human metapneumovirus-infected children was 11.6 months, the male:female ratio was 1.8:1, 78 percent of illnesses occurred between December and April, and the hospitalization rate was 2 percent. The virus was associated with bronchiolitis in 59 percent of cases, pneumonia in 8 percent, croup in 18 percent, and an exacerbation of asthma in 14 percent. We also detected human metapneumovirus in 15 percent of samples from 261 patients with upper respiratory tract infection but in only 1 of 86 samples from asymptomatic children.

CONCLUSIONS

Human metapneumovirus infection is a leading cause of respiratory tract infection in the first years of life, with a spectrum of disease similar to that of respiratory syncytial virus.

Bronchiolitis caused by respiratory syncytial virus in an area of portugal: epidemiology, clinical features, and risk factors

The aim of the present study was to analyse the clinical and epidemiological characteristics of bronchiolitis caused by respiratory syncytial virus (RSV) in 225 children observed in a paediatric hospital in Lisbon, Portugal, and to determine the clinical, epidemiological, or laboratory parameters that correlate with greater severity of the disease. This prospective study included hospitalised and ambulatory children younger than 36 months of age with a diagnosis of bronchiolitis and was conducted during two consecutive RSV epidemiological seasons (November-March 2000/01 and 2001/02). The median age of the patients was 5 months, and the male-to-female ratio was 1.6:1. RSV was isolated in 60.9% of patients, predominantly in the hospitalised group. The subtype A:B ratio was 7.4:1 and was similar in both seasons. RSV-positive patients were younger, had more severe clinical forms of bronchiolitis, and fewer changes in leucocyte total and differential counts. Among infected patients, higher clinical severity scores occurred in association with first wheezing episodes, overcrowded households, attendance at day-care centres, or prematurity (<36 weeks). This first prospective study of RSV epidemiology in Portugal provides a foundation for appropriate surveillance programmes of RSV infection in this country. A multicentre study is desirable in order to delineate optimal prophylactic and therapeutic guidelines for RSV infection in Portugal.

RSV-induced bronchiolitis but not upper respiratory tract infection is accompanied by an increased nasal IL-18 response

The aim of this study was to investigate potential differences in the local nasal immune response between bronchiolitis and upper respiratory tract infection induced by respiratory syncytial virus (RSV). Nasal brush samples were obtained from 14 infants with RSV bronchiolitis and from 8 infants with RSV upper respiratory tract infection. The samples were taken during infection (acute phase) and 2-4 weeks later (convalescent phase). Cytospin preparations were stained immunohistochemically for T cells, macrophages, and eosinophils. Staining also took place for intercellular adhesion molecule-1 (ICAM-1), T-helper 1 (Th1)-like (interleukin-12 [IL-12], interferon-gamma [IFN-gamma]), Th2-like (IL-4, IL-10), and proinflammatory cytokines (IL-6, IL-8, IL-18). During both RSV-induced bronchiolitis and upper respiratory tract infection, cellular inflammation was observed. This was characterised by an increase in the numbers of nasal macrophages, which tended to be higher in bronchiolitis than in upper respiratory tract infection. Numbers of T lymphocytes and ICAM-1 positive cells increased during both bronchiolitis and upper respiratory tract infection. There were no differences between numbers in the groups. Interestingly, a distinct nasal proinflammatory cytokine response was observed in RSV-induced bronchiolitis. This is characterised by an increase in the number of IL-18 positive cells. This increase is specific for bronchiolitis, as a similar increase could not be detected in RSV-induced upper respiratory tract infection. Numbers of IL-6 and IL-12 positive cells were higher in both bronchiolitis and upper respiratory tract infection, and there were no differences between the groups. By contrast, the number of IL-8, IFN-gamma, IL-4, and IL-10-positive cells remained constant. In conclusion, clear differences were found in nasal immune responses of children with RSV-induced upper respiratory tract infection or bronchiolitis. The induction of a strong IL-18 response was typical for bronchiolitis, as this could not be observed in RSV-induced upper respiratory tract infection, and could explain the eosinophilia that is observed frequently during bronchiolitis.

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.

Epidemiology and clinical presentation of respiratory syncytial virus infection in a rural area of southern Mozambique

BACKGROUND

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infection (LRTI) in infants throughout most of the world, but little is known about RSV infection in Africa where LRTI are among the leading causes of infant and childhood death.

METHODS

The study took place in a rural district hospital in southern Mozambique between October, 1998, and May, 2000. From all children (n = 5635) <1 year of age presenting to an outpatient department with cough or nasal secretion and all children (n = 1307) <5 years of age admitted to hospital with a LRTI, a nasopharyngeal aspirate was collected and tested for RSV by enzyme-linked immunosorbent assay (Abbott).

RESULTS

RSV infection was found in 8.6% of study infants in the outpatient department and 10.6% of admitted children with LRTI. Cases presented in predictable yearly outbreaks during the warm and rainy season. Lower respiratory tract involvement was frequent (59.7%). Cough, chest indrawing and increased respiratory rate were all independently related to RSV infection. Wheezing was infrequent. Bacterial coinfection (4.6%) and the case-fatality rate (3.4%) were low.

CONCLUSIONS

There is a substantial burden of disease attributable to RSV infection in this rural African setting, with the highest incidence and severity occurring in young infants.

Prophylactic effect of inactivated influenza vaccine on young children

BACKGROUND

The effectiveness of inactivated influenza vaccine in healthy infants and young children has been controversial. The aim of this study was to determine the prophylactic effect of inactivated influenza vaccine in young children.

METHODS

Eighty-six healthy infants and children younger than 7-years-old were immunized by a subcutaneous injection of inactivated influenza vaccine before the 1999/2000 influenza season. Ninety-four age-matched children were randomly assigned as the control. These children were followed-up from January to April, 2000. A diagnosis of influenza A virus infection was made rapidly by a positive result of the the enzyme immunoassay membrane test using enzyme-conjugated monoclonal antibodies specific for a conserved epitope of influenza A nucleoprotein. The incidence of influenza A infection was compared and statistically assessed.

RESULTS

The prevalence of influenza A virus infection, diagnosed by the influenza A rapid detection test, was 5.8% in the vaccine group and 17.0% in the control group, that is significantly lower in the vaccine receiving group than the non-receiving group (P = 0.016). However, four out of five infected children in the vaccine group were younger than 2-years-old.

CONCLUSION

We conclude that inactivated influenza vaccine reduces the incidence of influenza A virus infection in 2-6-year-old children.

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.

The effect of influenza on hospitalizations, outpatient visits, and courses of antibiotics in children

BACKGROUND

Despite high annual rates of influenza in children, influenza vaccines are given to children infrequently. We measured the disease burden of influenza in a large cohort of healthy children in the Tennessee Medicaid program who were younger than 15 years of age.

METHODS

We determined the rates of hospitalization for acute cardiopulmonary conditions, outpatient visits, and courses of antibiotics over a period of 19 consecutive years. Using the differences in the rates of these events when influenzavirus was circulating and the rates from November through April when there was no influenza in the community, we calculated morbidity attributable to influenza. There was a total of 2,035,143 person-years of observation.

RESULTS

During periods when influenzavirus was circulating, the average number of hospitalizations for cardiopulmonary conditions in excess of the expected number was 104 per 10,000 children per year for children younger than 6 months of age, 50 per 10,000 per year for those 6 months to less than 12 months, 19 per 10,000 per year for those 1 year to less than 3 years, 9 per 10,000 per year for those 3 years to less than 5 years, and 4 per 10,000 per year for those 5 years to less than 15 years. For every 100 children, an annual average of 6 to 15 outpatient visits and 3 to 9 courses of antibiotics were attributable to influenza. In winter, 10 to 30 percent of the excess number of courses of antibiotics occurred during periods when influenzavirus was circulating.

CONCLUSIONS

Healthy children younger than one year of age are hospitalized for illness attributable to influenza at rates similar to those for adults at high risk for influenza. The rate of hospitalization decreases markedly with age. Influenza accounts for a substantial number of outpatient visits and courses of antibiotics in children of all ages.