children <3 years of age attending two health centers , one public reference hospital ( joao alves ) , and a private hospital in aracaju were invited to participate in our study during april and may 2002 .
these months correspond to the beginning of the rainy season , when most cases of bronchiolitis occur .
the health centers provide 24-hour medical services for acute illnesses ; patients with severe health problems are referred to the public hospital .
the small private hospital caters to self - referred and transferred patients ( mostly from the public hospital ) .
children with diagnoses of acute lower respiratory infections ( alri ) were recruited consecutively after informed parental consent .
the diagnosis of alri was based on the presence of cough , tachypnea , chest indrawing , or wheeze of < 7 days duration and followed the world health organization s standard protocol for research on alri ( 14 ) .
nasopharyngeal secretions were collected by using sterile mucous traps ( maesk medical a / s , bettina bay , denmark ) . immediately after collection
, aspirates were mixed with phosphate - buffered saline , transferred into 2-ml cryotubes , and kept frozen at 80c until analyzed .
hypoxia levels were measured by pulse oximetry before the use of oxygen , and children were treated according to local guidelines for the management of alri .
detection of the hmpv genome was performed by reverse transcription  polymerase chain reaction amplification ( rt - pcr ) of the matrix ( m ) , fusion ( f ) and nucleocapsid ( n ) protein genes , as described previously ( 5 ) .
selected pcr products were cloned into a ta cloning vector ( pgem - t , promega , uk ) , and the sequence was determined to confirm the identity of the virus detected by the pcr reaction .
samples were defined as hmpv positive if at least two of the rt - pcr test results were positive , although in practice all positive samples had at least two positive pcrs .
a total of 111 children ( 57 from the health centers , 25 from joao alvez hospital , and 29 from the private hospital ) were recruited .
fifty - three ( 48% ) children were infected with rsv alone , 19 ( 17% ) with hmpv alone , and 8 ( 7% ) with both ( co - infections ) .
forty - six ( 88% ) of the rsv cases were of group a and 6 ( 12% ) group b. the incidence of alri increased during the 10 weeks of the study from no cases in the first 2 weeks , 4 cases in the next 2 weeks , and up to 25 cases in week 9 ( figure 1 ) .
rsv and hmpv infections appeared to coincide in time during the period of the study .
number of children with respiratory syncytial virus ( rsv ) , human metapneumovirus ( hmpv ) , and rsv / hmpv co - infection by study week ( week 10 incomplete ) .
eighteen ( 32% ) of the 57 patients attending the health centers had hmpv compared to 1 ( 4% ) of the 25 infants attending the reference hospital ( p = 0.01 ) .
in contrast , rsv was significantly ( p = 0.01 ) more frequently detected in patients attending the referral hospital ( 17 [ 68% ] of 25 ) than the health centers ( 23 [ 40% ] of 57 ) . the age distribution of the infected infants is shown in figure 2 .
the greatest number of cases of rsv was observed in children < 12 months of age .
hmpv infection appeared to be more frequent in children 624 months of age , although this finding was not statistically significant . figures are frequencies ( % ) , unless otherwise specified . 
number of children with respiratory syncytial virus ( rsv ) , human metapneumovirus ( hmpv ) , and rsv / hmpv co - infection by age .
all children had coughing ; 61 ( 55% ) were wheezing , which was audible without auscultation ; and 34 ( 31% ) had chest indrawing .
the mean respiratory rate on consultation was higher in patients with rsv than in patients with hmpv infection ( p = 0.03 ) .
similarly , wheezing was more often audible in children infected with rsv ( 59% ) than in children with hmpv ( 47% ) or rsv / hmpv co - infections ( 25% ) , although this finding did not reach statistical significance ( chi square for trend , p = 0.07 ) . eighteen ( 16% ) children had severe hypoxia with po2 90% , and 44 ( 40% ) had po2 < 94% .
five ( 26% ) of the 19 children with hmpv had po2 < 94% compared to 25 ( 47% ) of the 53 with rsv and 5 ( 63% ) of the 8 with rsv / hmpv co - infection ( chi square for trend , p = 0.05 ) .
severe hypoxia ( po2 < 90% ) , however , was less frequent in children with hmpv ( 1 [ 5% ] of 19 ) or rsv / hmpv co - infections ( 1 [ 13% ] of 8) than in children with rsv infection ( 14 [ 26% ] of 53 ( chi square for trend , p = 0.04 )
. the lower prevalence of hypoxia suggests that children with hmpv had milder illnesses , since only 5 ( 26% ) of the 19 hmpv patients and 2 ( 25% ) of the 8 patients with rsv / hmpv co - infections were admitted to hospital compared with 27 ( 51% ) of the 53 with rsv infection , although this finding was not statistically significant .
this study is the first to describe hmpv in latin america . to date , information on the clinical signs and symptoms and epidemiology of hmpv infection is limited .
our study indicates that hmpv and rsv may have similar signs and symptoms and can present as a co - infection .
the incidence of hmpv increased at the same time that the number of cases with rsv was increasing .
hmpv , however , was more prevalent in children attending peripheral clinics than the referral hospital .
similarly , children with hmpv were less likely to be hypoxic and had lower respiratory rates than those with rsv , which suggests that hmpv infection may result in milder clinical signs and symptoms .
further studies , however , are necessary to explore if coinfected children are more or less likely to have a worse clinical outcome than children infected with only one virus .
a recent report of hospitalized children in intensive care suggested that dual infections could be associated with increased severity ( 5 ) .
an alternative explanation to reconcile these findings is the possibility that different hmpv subgroups ( 2,9,10,13,16 ) produce clinical syndromes of varying severity .
caution is necessary to interpret our findings as this was a cross - sectional study .
virus in nasopharyngeal secretions does not prove that it is the cause of the respiratory symptoms , as we did not investigate the prevalence of the virus in asymptomatic children or the natural history of the infection .
hmpv , however , has been associated with community - acquired respiratory illnesses ( 2,6,912 ) and severe alri in immunocompromised patients ( 17,18 ) , and the virus was likely responsible for the clinical illness in our children .
several studies have also described an association between hmpv and acute wheezing ( 35,8 ) . although wheezing was a feature in 47% of the hmpv - infected children , a greater proportion ( 59% ) of children infected with rsv had wheezing .
the association between rsv infection and asthma is well studied . however , most children are exposed to rsv infections before the age of 2 years , and a combination of factors is likely required ( 19 ) . the coincidental timing of rsv and hmpv might have led us to miss the true cause . the role of hmpv in alri and asthma merits further investigation .
future studies should aim to establish the natural history and clinical outcome of these infections .
 we describe the epidemiologic and clinical characteristics of 111 children attending clinics and hospitals in aracaju , northeast brazil , with acute respiratory infections attributable to human metapneumovirus ( hmpv ) , respiratory syncytial virus ( rsv ) , or both in may and june 2002 . 
 fifty - three ( 48% ) children were infected with rsv alone , 19 ( 17% ) with hmpv alone , and 8 ( 7% ) had rsv / hmpv co - infections . 
The Study
Conclusions