after the first report to public health authorities of poultry outbreaks on february 18 , 2004 , enhanced surveillance for conjunctivitis and influenzalike illnesses was implemented for federal workers , farm workers and their household contacts , and any other potentially exposed persons . illness was reported to the british columbia centre for disease control by using a standard questionnaire and report form . respiratory specimens were tested at the british columbia centre for disease control by reverse transcription  polymerase chain reaction for influenza and by cell culture for all respiratory pathogens ; influenza isolates were sequenced to determine the subtype ( e.g. , h7 ) . suspected human cases were defined as illness in persons presenting after february 6 , 2004 , with two or more new or worsening conjunctivitis or influenzalike symptoms , with onset from 1 day after first exposure ( defined as direct contact or shared air space ) to 7 days after last exposure to a potential source of avian influenza virus in the fraser valley . confirmed cases had laboratory - confirmed influenza a ( h7 ) virus in conjunctival , nasal , nasopharyngeal , or throat specimens by reverse transcription  polymerase chain reaction ( 6 ) or cell culture . serum samples were tested for antibody to influenza a ( h7 ) by hemagglutination inhibition and microneutralization assays ( 7 ) at the national microbiology laboratory . centers for disease control and prevention on serum samples from two persons with confirmed infections and from eight persons with suspected cases . approximately 2,000 poultry farm workers are in the fraser valley . approximately 650 federal workers assisted with outbreak management and control ; not all had poultry exposure . from february 18 to june 1 , 2004 , a total of 77 symptomatic persons were reported to the british columbia centre for disease control . fifty - seven had suspected ( n = 55 ) or confirmed ( n = 2 ) avian influenza infections . among the 20 reports that did not meet the suspected or confirmed case definitions , 9 had insufficient information to determine case status , 3 did not meet the symptom requirements , 3 did not have a relevant exposure history , 1 had onset before february 6 , 3 had onset > 7 days after exposure , and 1 had onset < 1 day after exposure . baseline characteristics are shown in table 1 , and the epidemic curve is shown in the figure . twelve ( 22% ) reported taking prophylactic oseltamivir at symptom onset , and 11 ( 20% ) received oseltamivir for treatment . the remaining 22 patients with suspected cases were identified > 48 hours after onset or refused treatment . onset of symptoms for suspected and confirmed cases in humans and identification of infected commercial poultry flocks , highly pathogenic avian influenza h7n3 , british columbia , 2004 . date for poultry flock is either the date the flock was suspected to be infected ( because of clinical illness ) or the date the sample was taken as part of surveillance . respiratory specimens ( nasal , nasopharyngeal , throat , and conjunctival ) were collected from 47 patients with suspected cases ( 86% ) an average of 5 days after onset ( range 027 days ) . cell culture identified pathogens in two persons : adenovirus type 3 in one ( conjunctival and nasal specimens ) and hsv-1 in another ( throat specimen ) . no antibody to influenza a h7 could be detected in paired acute- and convalescent - phase serum samples ( n = 17 ) , drawn an average of 9 days ( range 033 days ) and 31 days ( range 1888 days ) after onset , respectively , or in convalescent - phase serum samples ( n = 8) drawn an average of 28 days ( range 856 ) after onset from patients with suspected cases . influenza a h7n3 infection was confirmed in two men ( 40 and 45 years of age ) exposed on different farms march 13 and march 2223 . both had direct conjunctival contact with infected poultry . one was not wearing eye protection , and the other was wearing glasses that were bypassed by a feather . conjunctivitis and coryza developed in the first patient , and conjunctivitis and headache developed in the second . influenza a h7n3 virus was isolated from a nasal specimen from one man ( a / canada/444/04 ) and a conjunctival specimen from the other ( a / canada/504/04 ) ; both samples were collected within 1 day of onset . no antibody to influenza a h7 could be detected by hemagglutination inhibition or microneutralization assays in serum samples collected 34 days and 8 and 22 days after onset , respectively . virus isolated from birds on the same source farm as the human isolate a / canada/444/04 was confirmed as hpai h7n3 by genotyping and ivpi . virus from birds on the same source farm as a / canada/504/04 showed insertion sequence match with hpai h7n3 , but ivpi was not performed ( c. kranendonk , national centre for foreign animal disease , pers . both human isolates contained an insertion sequence similar to that seen only in the hpai avian virus . these insertion sequences vary from the poultry virus by one and two amino acid differences , respectively . based on the consensus sequence for hpai h7 viruses , although enhanced surveillance identified 57 persons meeting a suspected case definition , avian influenza infection was confirmed in only 2 . the two patients had conjunctivitis and mild , influenzalike illnesses , similar to symptoms reported from the netherlands in association with another h7 subtype ( h7n7 ) ( 9 ) . neither confirmed case in british columbia mounted a hemagglutination inhibition or serum neutralizing antibody response . this finding has been observed elsewhere in association with avian influenza infection ( 10,11 ) . mechanical trauma , irritation due to dust or airborne particulate matter , or an allergic cause of symptoms associated with viral contamination , rather than infection , is less likely given the delay to symptom onset , consistent with the incubation period for influenza . among suspected cases , respiratory rather than conjunctival symptoms predominated . other pathogens were also detected among suspected case reports , a finding consistent with the relatively nonspecific case definition applied . from february 6 to may 21 , 2004 , routine influenza surveillance activities in the fraser valley also identified human influenza a from nine persons and two long - term care facility outbreaks . although no coinfections were identified , this human influenza activity increased concerns about potential mixture of avian influenza with human influenza strains . avian influenza h7 has caused human illness previously , most notably 89 confirmed human infections , including one death in the netherlands in 2003 ( 9 ) . based on the precedent set by the netherlands in protecting exposed persons , british columbia recommended comprehensive precautions for workers early in the outbreak . the strain circulating in british columbia may have been more limited in its ability to cause human illness . the genomic sequence of the avian viruses from the source farms of the two human isolates was consistent with hpai , whereas one of the human isolates was consistent with lpai . the presence of an insertion sequence in the human lpai isolate likely signifies that the virus in poultry mutated from hpai to lpai , and both were circulating among the birds on that source farm , the latter undetected . a less likely explanation is that mutation from hpai to lpai occurred in the human host . to date , illness in humans from h7 subtypes differs markedly in severity from that of avian influenza h5n1 ( 12 ) . their lower virulence should not be inferred to indicate lower pandemic potential since subclinical or mild infections may have greater opportunity through surreptitious spread to reassort and through mutation to become more virulent . a compilation and detailed overview of the protective measures used in all avian influenza outbreaks would help to estimate the actual risk to persons and populations . recommendations for precautions that are both necessary and reasonable during future poultry outbreaks could then be refined .
avian influenza that infects poultry in close proximity to humans is a concern because of its pandemic potential . in 2004 , 
 an outbreak of highly pathogenic avian influenza h7n3 occurred in poultry in british columbia , canada . 
 surveillance identified two persons with confirmed avian influenza infection . 
 symptoms included conjunctivitis and mild influenzalike illness .