It’s been a busy couple weeks, and tomorrow we’re heading out for a week’s vacation. I don’t know what my internet access will be like, but probably not too good, so this might be the last Mystery Rays post for 2009.

Quick notes from a series of articles in New England Journal of Medicine on disease caused by the pandemic swine-origin influenza virus:

… the majority of those infected have a mild illness. The typical period during which the virus can be detected with the use of real-time RT-PCR is 6 days (whether or not fever is present). The duration of infection may be shortened if oseltamivir is administered1

I bolded the part about oseltamivir (Tamiflu) because of the recent controversy (see the Avian Flu Diary, here and here) about Tamiflu’s effectiveness.

But even though the pandemic is usually mild, several groups are at unusual risk:

2009 H1N1 influenza can cause severe illness and death in pregnant and postpartum women; regardless of the results of rapid antigen testing, prompt evaluation and antiviral treatment of influenza-like illness should be considered in such women. The high cause-specific maternal mortality rate suggests that 2009 H1N1 influenza may increase the 2009 maternal mortality ratio in the United States. 2


Pandemic 2009 H1N1 influenza was associated with pediatric death rates that were 10 times the rates for seasonal influenza in previous years … Most deaths were caused by refractory hypoxemia in infants under 1 year of age (death rate, 7.6 per 100,000). 3

There’s an emerging sense that much of the young-person mortality associated with the pandemic flu4 is due fairly directly to the virus itself, rather than to subsequent bacterial infection.   That was probably not true for the 1918 influenza pandemic, where bacterial infections were a major part of the high mortality rates:

… bacterial infections, especially pneumococcal infections, were a major cause of influenza- associated pneumonia and death among both military personnel and civilians in 1918–1919. The distribution of pneumococcal serotypes shifted toward less invasive serotypes during that period as compared with the pre-1918 period, suggesting that the 1918 influenza virus increased host susceptibility to less-invasive pneumococci.5

And, as the authors note, underdeveloped countries may have higher mortality from the present pandemic, if there’s more risk of bacterial superinfection.

  1. Cao, B., Li, X., Mao, Y., Wang, J., Lu, H., Chen, Y., Liang, Z., Liang, L., Zhang, S., Zhang, B., Gu, L., Lu, L., Wang, D., Wang, C., & , . (2009). Clinical Features of the Initial Cases of 2009 Pandemic Influenza A (H1N1) Virus Infection in China New England Journal of Medicine, 361 (26), 2507-2517 DOI: 10.1056/NEJMoa0906612[]
  2. Janice K. Louie, Meileen Acosta, Denise J. Jamieson, Margaret A. Honein, & for the California Pandemic (H1N1) Working Group (2009). Severe 2009 H1N1 Influenza in Pregnant and Postpartum Women in California New England Journal of Medicine[]
  3. Romina Libster, & et al. (2009). Pediatric Hospitalizations Associated with 2009 Pandemic Influenza A (H1N1) in Argentina New England Journal of Medicine[]
  4. At least, in those places where autopsies have been consistently performed; which is biased against underdeveloped countries[]
  5. Chien, Y., Klugman, K., & Morens, D. (2009). Bacterial Pathogens and Death during the 1918 Influenza Pandemic New England Journal of Medicine, 361 (26), 2582-2583 DOI: 10.1056/NEJMc0908216[]