Background During 2004, a highly pathogenic avian
influenza A (H5N1) virus caused poultry disease in eight Asian countries
and infected at least 44 persons, killing 32; most of these persons
had had close contact with poultry. No evidence of efficient person-to-person
transmission has yet been reported. We investigated possible person-to-person
transmission in a family cluster of the disease in Thailand.
Methods For each of the three involved patients,
we reviewed the circumstances and timing of exposures to poultry
and to other ill persons. Field teams isolated and treated the surviving
patient, instituted active surveillance for disease and prophylaxis
among exposed contacts, and culled the remaining poultry surrounding
the affected village. Specimens from family members were tested
by viral culture, microneutralization serologic analysis, immunohistochemical
assay, reverse-transcriptase–polymerase-chain-reaction (RT-PCR)
analysis, and genetic sequencing.
Results The index patient became ill three to
four days after her last exposure to dying household chickens. Her
mother came from a distant city to care for her in the hospital,
had no recognized exposure to poultry, and died from pneumonia after
providing 16 to 18 hours of unprotected nursing care. The aunt also
provided unprotected nursing care; she had fever five days after
the mother first had fever, followed by pneumonia seven days later.
Autopsy tissue from the mother and nasopharyngeal and throat swabs
from the aunt were positive for influenza A (H5N1) by RT-PCR. No
additional chains of transmission were identified, and sequencing
of the viral genes identified no change in the receptor-binding
site of hemagglutinin or other key features of the virus. The sequences
of all eight viral gene segments clustered closely with other H5N1
sequences from recent avian isolates in Thailand.
Conclusions Disease in the mother and aunt probably resulted from
person-to-person transmission of this lethal avian influenzavirus
during unprotected exposure to the critically ill index patient.
From the Bureau of Epidemiology (K.U., C.P.), the Departments of
Medical Sciences (R. Kitphati, W.A., P.T., M.C.) and Disease Control
(S.C.), and the Kamphang Phet Hospital (R. Khontong), Thai Ministry
of Public Health, Nonthaburi, Thailand; the Faculty of Medicine,
Siriraj Hospital, Mahidol University, Bangkok, Thailand (P.A., P.P.,
M.U., K.B.); the International Emerging Infections Program, Thai
Ministry of Public Health and U.S. Centers for Disease Control and
Prevention, Nonthaburi, Thailand (S.F.D., J.M.S.); and the Centers
for Disease Control and Prevention, Atlanta (N.J.C., S.R.Z.).
Address reprint requests to Dr. Ungchusak at the Bureau of Epidemiology,
Department of Disease Control, Ministry of Public Health, Tivanon
Rd., Nonthaburi 11000, Thailand, or at firstname.lastname@example.org.
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