BCCDC responds

A cardinal feature of influenza illness is its short incubation and sudden onset. For seasonal influenza viruses, the incubation period is generally estimated to be 1- to 4-days.[1] The 2009 swine-origin pandemic A/H1N1 (pH1N1) virus is considered a novel pathogen, but it is nevertheless an influenza virus and anticipated to share consistent epidemiologic characteristics. Published data estimating the specific incubation period for pH1N1 are limited but nevertheless consistent with this typical 1- to 4-day range, with some series suggesting an upper limit of 7 days.[2-4]

In light of these observations, the US Centers for Disease Control and Prevention,[5] European Centre for Disease Control,[6] and the World Health Organization[7] each currently cite an incubation period of 1 to 7 days for pH1N1, acknowledging up to 4 days is a more likely range. The Public Health Agency of Canada also initially advised of a 1- to-7 day incubation period but has recently revised its guidelines to specify 1 to 4 days as most likely.[8] Thus, even doubling the likely incubation period as a margin of error, most people may consider themselves “out of the woods” if still asymptomatic at 1 week following specific pH1N1 exposure.

—Danuta M. Skowronski, MD
—Travis Hottes, MSc
Influenza & Emerging Respiratory Pathogens Team
BC Centre for Disease Control


1. Lessler J, Reich NG, Brookmeyer R, et al. Incubation periods of acute respiratory viral infections: A systematic review. Lancet Infect Dis 2009;9:291-300.
2. Dawood FS, Jain S, Finelli L, et al. Emergence of a novel swine-origin influenza A (H1N1) virus in humans. N Engl J Med 2009;360: 2605-2615.
3. Jeannot AC, Hamoudi M, Bourayou N, et al. Premiers cas de transmission secondaire en France du nouveau virus grippal d’origine porcine A(H1N1)v. Médecine et maladies infectieuses 2009;doi:10.1016/j.medmal. 2009.06.014.
4. Odaira F, Takahashi H, Toyokawa T, et al. Assessment of secondary attack rate and effectiveness of antiviral prophylaxis among household contacts in an influenza A(H1N1)v outbreak in Kobe, Japan, May - June 2009. Eurosurveillance 2009;14(35).
5. US CDC. Interim guidance for clinicians on identifying and caring for patients with swine-origin influenza A(H1N1) virus infection. cdc.gov/h1n1flu/identifyingpatients.htm (accessed 15 September 2009).
6. European Centre for Disease Prevention and Control. ECDC Interim Risk Assessment: Influenza A(H1N1) 2009 Pandemic. 20 July 2009. ecdc.europa.eu/en/health topics/Documents/0908_Influenza_AH1N1_Risk_Assessment.pdf (accessed 15 September 2009).
7. World Health Organization. Transcript of virtual press conference with Gregory Hartl, WHO Spokesperson for Epidemic and Pandemic Diseases, and Dr. Keiji Fukuda, Assistant Director-General ad. Interim for Health Security and Environment, WHO. 04 May 2009. www.who.int/mediacentre/swineflu_presstranscript_2009_05_04.pdf (accessed 15 September 2009).
8. Public Health Agency of Canada. Individual and community based measures to help prevent transmission of influenza-like illness (ILI) in the community, including the pandemic influenza (H1N1) 2009 virus. 10 September 2009. phac-aspc.gc.ca/alert-alerte/h1n1/hp-ps-info_health-sante-eng.php (accessed 15 September 2009).

Danuta M. Skowronski, MD, FRCPC, Travis Hottes, MSc,. BCCDC responds. BCMJ, Vol. 51, No. 8, October, 2009, Page(s) 335 - Letters.

Above is the information needed to cite this article in your paper or presentation. The International Committee of Medical Journal Editors (ICMJE) recommends the following citation style, which is the now nearly universally accepted citation style for scientific papers:
Halpern SD, Ubel PA, Caplan AL, Marion DW, Palmer AM, Schiding JK, et al. Solid-organ transplantation in HIV-infected patients. N Engl J Med. 2002;347:284-7.

About the ICMJE and citation styles

The ICMJE is small group of editors of general medical journals who first met informally in Vancouver, British Columbia, in 1978 to establish guidelines for the format of manuscripts submitted to their journals. The group became known as the Vancouver Group. Its requirements for manuscripts, including formats for bibliographic references developed by the U.S. National Library of Medicine (NLM), were first published in 1979. The Vancouver Group expanded and evolved into the International Committee of Medical Journal Editors (ICMJE), which meets annually. The ICMJE created the Recommendations for the Conduct, Reporting, Editing, and Publication of Scholarly Work in Medical Journals to help authors and editors create and distribute accurate, clear, easily accessible reports of biomedical studies.

An alternate version of ICMJE style is to additionally list the month an issue number, but since most journals use continuous pagination, the shorter form provides sufficient information to locate the reference. The NLM now lists all authors.

BCMJ standard citation style is a slight modification of the ICMJE/NLM style, as follows:

  • Only the first three authors are listed, followed by "et al."
  • There is no period after the journal name.
  • Page numbers are not abbreviated.

For more information on the ICMJE Recommendations for the Conduct, Reporting, Editing, and Publication of Scholarly Work in Medical Journals, visit www.icmje.org

BCMJ Guidelines for Authors

Leave a Reply