Early pandemic influenza (2009 H1N1) in Ho Chi Minh City, Vietnam: a clinical virological and epidemiological analysis.
BACKGROUND
To date, little is known about the initial spread and response to the 2009 pandemic of novel influenza A ("2009 H1N1") in tropical countries. Here, we analyse the early progression of the epidemic from 26 May 2009 until the establishment of community transmission in the second half of July 2009 in Ho Chi Minh City (HCMC), Vietnam. In addition, we present detailed systematic viral clearance data on 292 isolated and treated patients and the first three cases of selection of resistant virus during treatment in Vietnam.


RESULTS
Data sources included all available health reports from the Ministry of Health and relevant health authorities as well as clinical and laboratory data from the first confirmed cases isolated at the Hospital for Tropical Diseases in HCMC. Extensive reverse transcription (RT)-PCR diagnostics on serial samples, viral culture, neuraminidase-inhibition testing, and sequencing were performed on a subset of 2009 H1N1 confirmed cases. Virological (PCR status, shedding) and epidemiological (incidence, isolation, discharge) data were combined to reconstruct the initial outbreak and the establishment of community transmission. From 27 April to 24 July 2009, approximately 760,000 passengers who entered HCMC on international flights were screened at the airport by a body temperature scan and symptom questionnaire. Approximately 0.15% of incoming passengers were intercepted, 200 of whom tested positive for 2009 H1N1 by RT-PCR. An additional 121 out of 169 nontravelers tested positive after self-reporting or contact tracing. These 321 patients spent 79% of their PCR-positive days in isolation; 60% of PCR-positive days were spent treated and in isolation. Influenza-like illness was noted in 61% of patients and no patients experienced pneumonia or severe outcomes. Viral clearance times were similar among patient groups with differing time intervals from illness onset to treatment, with estimated median clearance times between 2.6 and 2.8 d post-treatment for illness-to-treatment intervals of 1-4 d, and 2.0 d (95% confidence interval 1.5-2.5) when treatment was started on the first day of illness.


CONCLUSIONS
The patients described here represent a cross-section of infected individuals that were identified by temperature screening and symptom questionnaires at the airport, as well as mildly symptomatic to moderately ill patients who self-reported to hospitals. Data are observational and, although they are suggestive, it is not possible to be certain whether the containment efforts delayed community transmission in Vietnam. Viral clearance data assessed by RT-PCR showed a rapid therapeutic response to oseltamivir.
Hien
Tran Tinh
TT
Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Program, Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam.
Boni
Maciej F
MF
Bryant
Juliet E
JE
Ngan
Tran Thuy
TT
Wolbers
Marcel
M
Nguyen
Tran Dang
TD
Truong
Nguyen Thanh
NT
Dung
Nguyen Thi
NT
Ha
Do Quang
do Q
Hien
Vo Minh
VM
Thanh
Tran Tan
TT
Nhu
Le Nguyen Truc
le NT
Uyen
Le Thi Tam
le TT
Nhien
Pham Thi
PT
Chinh
Nguyen Tran
NT
Chau
Nguyen Van Vinh
NV
Farrar
Jeremy
J
van Doorn
H Rogier
HR
D000401:Aircraft; D004196:Disease Outbreaks; D018562:Disease Transmission, Infectious / Q000517:prevention & control / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000188:drug therapy / Q000453:epidemiology* / Q000635:transmission; D008403:Mass Screening; D053139:Oseltamivir / Q000627:therapeutic use; D013997:Time Factors; D014195:Travel; D014744:Vietnam / Q000453:epidemiology
D053139:Oseltamivir