in partnership with the government of bangladesh , the us centers for disease control and prevention ( cdc ) and the international centre for diarrhoeal disease research , bangladesh ( icddr , b ) established nationwide hospital - based surveillance to identify clusters of persons with life - threatening influenza virus infections ( 6 ) . additionally , icddr , b has had an urban field site in dhaka ( kamalapur ) , where population - based respiratory disease surveillance was begun in 1998 . in april 2004
the site and its surveillance system have been described ( 8) . as part of this surveillance , a blood culture for bacterial pathogens was collected from every child with acute respiratory or febrile illness , and from 1 in 5 ( 20% sampling frame ) a nasopharyngeal wash specimen was collected for influenza virus culture in mdck cells , and acute - phase and convalescent - phase serum samples were collected for detecting other respiratory viruses . on january 29 , 2008 , a 16-month - old boy was brought to the kamalapur clinic with a history of 7 days of fever , 5 days of cough and rhinorrhea , and 3 days of difficult / fast breathing and loss of appetite ( table ) .
she said he had not exhibited diarrhea , convulsions , or other signs of illness .
the child had been hospitalized 1 year earlier for acute watery diarrhea that resolved uneventfully .
no underlying illnesses had been diagnosed , and he had not received any medications before this clinic visit .
examination showed that the child had a fever , a mildly elevated respiratory rate , and a clear nasal discharge ( table ) .
blood for bacterial culture and viral serologic testing and a nasopharyngeal wash sample were collected according to accepted routine .
a chest radiograph showed scattered bilateral alveolar infiltrates . because of the duration of his fever
, he received a diagnosis of suspected typhoid fever , which is endemic to this community ( 9 ) , and was given oral amoxicillin and nystatin for oral thrush . at a follow - up visit to the clinic on january 31 , the patient was afebrile ; he was in no distress and had a lower respiratory rate ( 36 breaths / min ) .
the patient again visited the clinic on february 5 and february 10 and was afebrile on both occasions with a mildly elevated respiratory rate ( 38 breaths / min ) and clear lungs .
the mother reported that the child had had loose stools ( possibly associated with amoxicillin ) on february 10 , but she denied that he had diarrhea .
the child was never hospitalized ; he completed a 14-day course of amoxicillin for suspected enteric fever and recovered fully .
his blood culture was negative for any organism , and his final diagnosis was upper respiratory tract infection . on february 13 , a convalescent - phase serum sample was collected as part of routine surveillance .
culture of the child s nasopharyngeal wash sample showed cytopathic effects consistent with influenza virus infection ; an aliquot reacted to influenza virus a antiserum but not to antiserum to subtypes h1 or h3 .
an aliquot of the viral culture material was shipped frozen on april 22 , 2008 , to cdc , where the isolate was identified as hpai ( h5n1 ) virus by real - time reverse transcription  pcr .
the virus was identified as an h5n1 clade 2.2 strain on the basis of the hemagglutinin sequence ( figure ) .
after identification of the influenza virus isolate as hpai ( h5n1 ) in may 2008 , an epidemiologic investigation was initiated , and serum samples were collected from the child and 3 family members .
the child lived with both parents and a sister in a 1-room residence . in late january 2008
, the father had brought home a well - appearing live chicken from a local market located 50 m from the house .
the mother slaughtered the chicken inside the bathroom while the child slept ; she did not report having washed her hands before she handled the child .
the waste materials from the slaughter were then stored in a tied polyethylene bag near the house entrance for 2 hours before disposal .
microneutralization assay , using the child s subtype h5n1 isolate at cdc , demonstrated a 4-fold rise in subtype h5n1 neutralizing antibodies between the child s january 2008 serum specimens ( titer < 20/20 ) and may 2008 ( titer 160/80 ) serum specimens .
serum specimens from the child s family members tested seronegative for subtype h5n1 neutralizing antibodies ( the sister was away from the household in january ) .
the virus found in the child , a / bangladesh/207095/2008 , is indicated in boldface .
we report hpai ( h5n1 ) in a child in bangladesh ; the infection was confirmed by virus isolation from an upper respiratory specimen and by serologic testing .
one potential exposure was the healthy - appearing chicken that was brought inside the home .
the child did not have direct contact with the chicken , although indirect contact was suggested because his mother handled him after slaughtering the chicken .
the owner of the poultry shop where the chicken was purchased reported that 5%10% of chickens had died each day during january 2008 ( 10 ) .
because the shop was located 50 m from the home , environmental subtype h5n1 exposures can not be ruled out .
this virus was of the same clade and phylogenetic subgroup reported in poultry in bangladesh during this period ( 5 ) .
no other household members or neighbors reported illness , and no other family members had serologic evidence of subtype h5n1 infection . in nearly 25%
of reported subtype h5n1 cases worldwide , the exposure source is unclear ( 2 ) . in bangladesh and other countries with influenza ( h5n1 ) outbreaks among poultry , surveillance for human subtype h5n1 cases is focused on hospital - based case finding for febrile patients with severe acute respiratory illness .
this child was not suspected of having subtype h5n1 infection and had had no known poultry contact ; his illness would not have met standard criteria for subtype h5n1 testing ( 11 ) . instead
, an upper respiratory tract specimen was collected from the child as part of routine influenza surveillance among pediatric outpatients .
similar clinically mild cases of subtype h5n1 infection in children have been identified in turkey ( 12 ) , indonesia ( 13 ) , and egypt ( 2 ) .
the 1 in 5 sampling frame , a major limitation of this study , raises the possibility that undetected mild cases of subtype h5n1 infection have occurred in children in this population .
other limitations include the elapsed time between illness onset and investigation and the identification of only 1 case .
the public health value of identifying the cause of severe acute respiratory illness clusters with pandemic potential is clear .
this case highlights the value of routine outpatient surveillance for detecting both seasonal and novel influenza a viruses , particularly in settings in which subtype h5n1 strains circulate among poultry .
because exposure of subtype h5n1 to humans increases its opportunities for genetic mutation or reassortment , or both , with human influenza a viruses ( 3 ) , other surveillance strategies , including cross - sectional and longitudinal serosurveys among potentially exposed persons , can help inform the extent of , and risk for , asymptomatic and clinically mild subtype h5n1 infection .
 we identified avian influenza virus a ( h5n1 ) infection in a child in bangladesh in 2008 by routine influenza surveillance . 
 the virus was of the same clade and phylogenetic subgroup as that circulating among poultry during the period . 
 this case illustrates the value of routine surveillance for detection of novel influenza virus . 
The Study
Conclusions