Press Release
Update on Influenza A H5N1
January 23, 1998
Influenza A H5N1 is a new viral human pathogen first isolated in Hong Kong in 1997. The virus was previously known to infect birds only. As at 23 January 1998, there were 18 confirmed human cases. The onset date of the last case was on 28 December 1997. The distribution of onset dates is as follows:
mid-May 97 : 1
2-8 Nov 97 : 1
9-15 Nov 97: 0
16-22 Nov 97: 2
23-29 Nov 97: 1
30 Nov - 6 Dec 97: 1
7-13 Dec 97: 4
14-20 Dec 97: 5
21-27 Dec 97: 1
28 Dec 97 - 3 Jan 98: 1
Remarks: one case admitted to hospital on 28 Dec 1997 still under investigation
The 18 confirmed cases comprised 8 males and 10 females, age ranging from 1 to 60. Nine cases were children under 12. The cases came from different parts of the territory : 3 cases in Hong Kong Island, 6 cases in Kowloon, 3 in East New Territories and 6 in West New Territories.
The initial presentations of influenza A H5N1 are very similar to other influenza viruses, typically with fever, malaise, myalgia, sore throat and cough. However, conjunctivitis is seen in some patients. Persistent high fever (>39oC) is another useful sign that may alert health care workers of the possibility of H5N1 infection. The virus may cause a rapid downhill course in some cases, ending with viral pneumonia, respiratory distress syndrome and multi-organ failure. X-ray of the chest is useful in picking up early viral pneumonia which is also clinically detectable. Among the 18 confirmed cases, 6 have died, one is now in critical condition and one in fair condition.
Investigation of the first case indicated that the main mode of transmission of influenza A H5N1 was from bird to man. The possibility of man-to-man transmission is open; but even if it occurs, the efficiency of transmission is low at this time.
There was history of possible exposure to poultry in 7 out of the 18 confirmed cases. In one case, the school kept chickens and ducklings but there was no history of the patient coming into direct contact with these birds. Three patients had history of buying poultry from markets before onset of diseases. In another two cases, there were chicken stalls in the close vicinity of their living place and playing area. H5N1 viruses were also isolated from the chicken stalls. As for the remaining case, the patient frequently went to work in the market where there were chicken stalls although the history of petting chickens could not be recalled.
Temporary suspension of chicken import from the mainland began since 24 December 1997. From 29-31 December 1997, a exercise was carried out to slaughter all chicken in local chicken farms and all poultry at wholesale markets and retail outlets in Hong Kong.
There is at present no vaccine for influenza A H5N1. However, the virus is known to be sensitive to amantadine and rimantadine.
Cases summaries of the 18 confirmed H5N1 cases
Case No.1 was a 3 year-old boy who became ill on 11/5/97 with fever, sore throat and abdominal pain and was admitted to QEH on 16/5/97. He died of multiple medical complications including pneumonia, ARDS, Reye's Syndrome and liver and renal failure on 21/5/97. His school kept chickens and ducklings but there was no history of the patient coming into direct contact with these birds. Virus was isolated from tracheal aspirate taken on 19/5/97.
Case No.2 was a 2 year-old boy with ventricular septal defect. He developed high fever, cough, sore throat and running nose on 6/11/97 and was admitted to QMH on 7/11/97. Recovery was complete. He was discharged on 9/11/97. Virus was isolated from nasopharyngeal aspirate taken on 7/11/97.
Case No.3 was a 13 year-old girl who developed fever, sore throat, running nose, headache and cough on 20/11/97. She was admitted to PWH for treatment of pneumonia on 26/11/97. Her condition deteriorated rapidly and was put on mechanical ventilation in ICU. She died on 21/12/97 because of pneumonia and multi-organ failure. Direct IFA was positive and virus was isolated from tracheal aspirate taken on 26/11/97.
Case No.4 was a 54 year-old retired man who developed fever, chills, rigor, cough and shortness of breath on 24/11/97 and was admitted to QEH on 29/11/97. His condition deteriorated and he died on 5/12/97 of complications arising from pneumonia. He had been to Korea with a friend during 26 to 29/11/97. Virus was isolated from bronchoalveolar lavage taken on 1/12/97.
Case No.5 was a 5 year-old girl who developed fever, cough and vomiting on 7/12/97. Her symptoms persisted despite treatment. She was admitted to QMH on 10/12/97. Provisional diagnosis was tonsillitis. Recovery was complete. She was discharged on 29/12/97. There were chicken stalls in the close vicinity of her living place and playing area. Direct IFA using monoclonal antibody was positive and virus was isolated from nasopharyngeal aspirate taken on 11 & 13/12/97.
Case No.6 was a 37 year-old Office Assistant who developed chills, rigor, malaise and myalgia on 17/11/97. A few days later, he developed productive cough with blood-stained sputum. His symptoms persisted despite treatment and he was admitted to QEH on 24/11/97. Chest X-ray showed bilateral pleural effusion and patchy consolidation of both lower zones. Fulminant atypical pneumonia was diagnosed. His condition improved with treatment and he was discharged on 9/12/97. There were two poultry stalls on G/F of the building where he lived. He gave history of buying poultry from the market 2 days before the onset of illness. The case was diagnosed by a rise in antibody titre by microneutralization test on blood taken on 24 & 28/11/97 and 5/12/97.
Case No.7 was a 24 year-old Filipino domestic helper who developed fever, sore throat, headache, cough, dizziness, mild shortness of breath and loss of appetite on 4/12/97. She was admitted to Yan Chai Hospital on 7/12/97. Her condition deteriorated in the following days and she required ventilatory and inotropic support in ICU. Chest X-ray showed left lower zone consolidation. At present, her condition remained critical. IFA for H5 was positive and virus was isolated from tracheal aspirate taken on 8 & 12/12/97.
Case No.8 was a 2 year-old boy, a cousin of Case No.5. He developed fever, cough and running nose on 12/12/97 and was admitted to QMH on 13/12/97. Recovery was complete. He was discharged on 29/12/97. There were chicken stalls in the close vicinity of his living place and playing area. RT-PCR and IFA for flu A were positive and virus was isolated from throat swab taken on 12/12/97 and from nasopharyngeal aspirate taken on 13, 14 & 15/12/97.
Case No.9 was a 4 year-old boy who developed fever, cough and running nose on 10/12/97. As his symptoms persisted, he was admitted to Yan Chai Hospital on 13/12/97. He made a full recovery and was discharged on 31/12/97. Directigen for flu A was positive and virus was isolated from nasopharyngeal aspirate taken on 15/12/97.
Case No.10 was a 1 year-old boy who developed fever, cough and running nose on 16/12/97. He was admitted to TMH on 18/12/97. Recovery was complete. He was discharged on 20/12/97. Virus was isolated from nasopharyngeal aspirate taken on 18/12/97.
Case No.11 was a 3 year-old girl who developed fever, cough and running nose on 16/12/97. She was admitted to TMH first on 21/12/97 and discharged on 22/12/97, and then admitted again on 26/12/97 and discharged on the same day. Virus was isolated from throat swab taken on 22/12/97.
Case No.12 was a 60 years-old female who was admitted to UCH on 17/12/97 for fever, chills and, rigor since 16/12/97. She had history of malignant thymoma treated with radiotherapy. A heart murmur was detected. Provisional diagnosis was endocarditis and she was treated with antibiotics. Her condition deteriorated in the following few days. She was transferred to ICU on 21/12/97. Chest X-ray showed bilateral haziness. She died on 23/12/97. Directigen for flu A and monoclonal antibody for H5 were positive and virus was isolated from tracheal aspirate taken on 22/12/97.
Case No.13 was a 25 year-old female who developed fever, cough, headache, dizziness and arthralgia on 17/12/97 and was admitted to TMH on 21/12/97 for treatment of pneumonia. She was in respiratory failure and died on 14/1/98 of viral pneumonitis and ARDS. From 10/12/97, she had been buying chicken from Tin Yiu Market everyday. Directigen for flu A was positive and virus was isolated from nasopharyngeal aspirate and sputum taken on 24/12/97 and from tracheal aspirate taken on 25/12/97.
Case No.14 was a 14 year-old girl who developed cough, fever and running nose on 23/12/97 and was admitted to PMH on 26/12/97. She had history of histiocytosis X and diabetes insipidus. CXR showed haziness particularly on the left side. Her symptoms worsened after admission and was transferred to ICU on 29/12/97. Nevertheless, she made a full recovery and was discharged on 13/1/98. She worked at the vegetable stall run by the family in Shek Kep Mei market where there were chicken stalls everyday after school and on weekends, however history of petting chicken could not be recalled. Virus was isolated from nasopharyngeal aspirate taken on 28 & 29/12/97.
Case No.15 was a 3 year-old boy who developed fever, running nose and cough on 28/12/97 and was admitted to PMH on 2/1/98. His condition was satisfactory. He made a full recovery and was discharged on 11/1/98. Virus was isolated from throat swab taken on 29/12/97.
Case No.16 was a 19 year-old girl who developed fever and cough with whitish sputum on 14/12/97 and was admitted to YCH on 17/12/97. Her condition deteriorated and she required treatment in ICU. She was transferred to general ward on 15/1/98 and her condition was fair. Virus was isolated from nasopharyngeal aspirate taken on 21/12/97. Microneutralization test on blood taken on 19 & 27/12/97 was positive.
Case No.17 was a 6 year-old girl who developed fever, cough, running nose and sore throat on 7/12/97. She was admitted to KWH on 11/12/97. CXR on 13/12/97 revealed right lower lobe pneumonia. She responded to antibiotic treatment and was discharged on 22/12/97. She had history of contact with chicken at a market in Tuen Mun on 23/11/97. Microneutralization test on blood taken on 12 & 23/12/97 was positive.
Case No.18 was a 34 year-old female who developed fever, bed sore over left thigh, paraplegia and pleural effusion before 28/12/97 whence she was admitted to QEH. She had history of SLE with nephritis. CXR showed right lower zone haziness. On 7/1/98, her condition deteriorated with high swinging fever and was transferred to ICU because of respiratory failure. CXR showed bilateral haziness. Blood culture showed MRSA septicaemia. She developed septicaemic shock and convulsion on 11/1/98 and died on the same date. Virus was isolated from tracheal aspirate taken on 9/1/98.