Novel H1N1 influenza can cause severe respiratory illness, profound lung damage, and death even in patients with no underlying conditions to make them vulnerable, a team of physicians from Mexico report in a rush article published online today by the New England Journal of Medicine (NEJM).

The analysis of 18 patients hospitalized with H1N1 (swine) flu at the National Institute of Respiratory Diseases (INER) in Mexico during the pandemic's earliest days reveals that fewer than half had underlying medical conditions, but more than half needed mechanical ventilation within a day of admission. Seven of the 18 died.

In a companion article, also published in advance online today, a multi-national team from Mexico and the United States document the age distribution of the first month of the H1N1 pandemic in Mexico, where the disease appears to have struck first, and confirm its unusual pattern of severe pneumonia among younger patients. Matching the pattern to those of earlier pandemics, the team speculates on the "biologic plausibility of partial protection" in older people exposed to mid-20th century strains of seasonal flu.

The case series of 18 patients, written by researchers from INER, the Mexican Secretariat of Health and BIRMEX, Mexico's state-owned vaccine-production laboratories, documents the severe illness of the first patients admitted with lab-confirmed H1N1 infection and x-ray–confirmed bilateral pneumonia during the pandemic's first wave.

The 18, of whom 7 died, are a subset of 98 patients hospitalized at the institute with pneumonia or influenza-like illness between March 24, the presumed onset date of the first known case, and April 24. Those 98 were a subset of 214 patients who came to the institute's emergency room with influenza-like illness or severe respiratory distress.

Conclusions

The emergence of influenza A (H1N1) 91 years ago led to a disastrous global pandemic. That virus is thought to have emerged almost simultaneously from birds into humans and swine. In contrast, S-OIV probably emerged from swine into humans. Although the immediate genetic event that led to the emergence of the new pandemic threat was a reassortment between two influenza A (H1N1) swine viruses, these two viruses were actually the products of at least four independent avian-to-mammalian cross-species transmissions, with at least four previous reassortments of gene segments among avian, human, and swine-adapted viruses (Figure 2). One consequence of this intertwined history is that S-OIV shares three gene segments with current seasonal human influenza A (H1N1) virus and three segments with human seasonal influenza A (H3N2) virus. It is not known whether low levels of cross-immunity against historically remote shared epitopes might confer some clinical protection against the newly emerging virus.


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Figure 2. History of Human and Swine Influenza Lineages.

The diagram shows the full genetic history of the swine-origin influenza A (H1N1) virus (S-OIV). Each of the seven charts represents the genetic composition of a particular influenza virus lineage over time. In each chart, gene segments are shown along the left side, and dates from 1918 to 2009 are shown along the top. Color coding shows the avian origins and history of each gene segment in each influenza virus lineage. The influenza virus gene segment reassortments that gave rise to the H2N2 and H3N2 strains of human influenza A are shown on the left side of the diagram, along with human influenza A (H1N1) viruses or their descendants. Swine influenza A (H1N1) viruses are shown on the right side of the diagram.




The history of influenza A (H1N1) virus is punctuated by frequent, sporadic cross-species transmissions from swine to humans. Although the sporadically transmitted swine viruses are sufficiently pathogenic in humans to cause clinically apparent disease, they are rarely transmitted among humans. Exposure and infection are necessary but not sufficient for a new epidemic virus to emerge; the virus must also adapt and transmit.12 The one prominent exception to the general rule that these swine viruses are not transmitted among humans was the outbreak at Fort Dix. This virus was never transmitted beyond the military installation, probably because the intrinsic transmissibility of the virus was simply too low. Yet the global response to this outbreak was forceful, especially given that the outbreak self-quenched. The decision to mass-vaccinate the U.S. population resulted in the unfortunately large cluster of Guillain–Barré cases. Perhaps an even more serious consequence was the accidental release of human-adapted influenza A (H1N1) virus from a research study, with subsequent resurrection and global spread of this previously extinct virus, leading to what could be regarded as a "self-fulfilling prophecy" epidemic. The 1998 triple reassortant influenza A (H1N1) swine virus has shown what appears to be a proclivity to jump the species barrier and cause swine-to-human infections.

The emergence of yet another serious global health threat from an animal source highlights the critical need for deeper understanding of zoonotic viruses, including in vivo studies of pathogenesis in animals, field epidemiologic studies, and surveillance in animal populations, along with the development of computational models. The presumptive origins of the S-OIV influenza epidemic outside the United States show the critical importance of international collaboration in efforts to predict and control future pandemic threats.

Originally posted by PrisonerOfSociety
reply to post by asala

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Do you mean 'London town', that's a pretty big collective; can you be more specific as London is definitely one to watch.

Do you use the tube? Have you seen people wearing masks yet?

Schools break up for 6 weeks in 2 weeks, so it should be interesting if they try to keep them open until then.

Health experts have said Watford has been classified as a swine flu “hot spot” to help stop the spread of the virus.

Pupils at more schools across south west Hertfordshire have this afternoon been sent home with letters informing parents of outbreaks of the bug in classrooms.

Watford, Three Rivers and Hertsmere have all now been classified as epicentres for the virus, joining areas across London, near Birmingham and in Luton as those most severely infected.

A statement from the West Hertfordshire PCT read: “The Department of Health and the Health Protection Agency (HPA) have identified several areas in the UK where there is now widespread community transmission of swine flu - these are sometimes referred to as 'hotspots'.

“These areas now include the Watford, Three Rivers and Hertsmere district council areas in West Hertfordshire.

“In the same way as has already been done in parts of the West Midlands and London, the HPA has issued updated guidance to GPs in West Hertfordshire on how to handle cases of swine flu.

“From now on, GPs in these 'hotspots' will be using clinical assessment to determine who needs to be treated.

“This means that people who have flu-like symptoms may be clinically diagnosed as having swine flu without needing laboratory confirmation in all cases. GPs will then assess whether treatment is appropriate.”