United States Cen­ters for Dis­ease Con­trol and Pre­ven­tion. MMWR. 1 May 2013. 62:1–6.
Avail­able at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm62e0501a1.htm

Excerpt. On March 29, 2013, the Chi­nese Cen­ter for Dis­ease Con­trol and Pre­ven­tion com­pleted lab­o­ra­tory con­fir­ma­tion of three human infec­tions with an avian influenza A(H7N9) virus not pre­vi­ously reported in humans. These infec­tions were reported to the World Health Orga­ni­za­tion (WHO) on March 31, 2013, in accor­dance with Inter­na­tional Health Reg­u­la­tions. The cases involved two adults in Shang­hai and one in Anhui Province. All three patients had severe pneu­mo­nia, devel­oped acute res­pi­ra­tory dis­tress syn­drome (ARDS), and died from their ill­ness. The cases were not epi­demi­o­log­i­cally linked. The detec­tion of these cases ini­ti­ated a cas­cade of activ­i­ties in China, includ­ing diag­nos­tic test devel­op­ment, enhanced sur­veil­lance for new cases, and inves­ti­ga­tions to iden­tify the source(s) of infec­tion. No evi­dence of sus­tained human-to-human trans­mis­sion has been found, and no human cases of H7N9 virus infec­tion have been detected out­side China, includ­ing the United States. This report sum­ma­rizes recent find­ings and rec­om­men­da­tions for prepar­ing and respond­ing to poten­tial H7N9 cases in the United States. Clin­i­cians should con­sider the diag­no­sis of avian influenza A(H7N9) virus infec­tion in per­sons with acute res­pi­ra­tory ill­ness and rel­e­vant expo­sure his­tory and should con­tact their state health depart­ments regard­ing spec­i­men col­lec­tion and facil­i­ta­tion of con­fir­ma­tory testing.

Zhuang QY, Wang SC, Wu ML, et al. Chi­nese Sci­ence Bul­letin. 29 April 2013. doi: 10.1007/s11434-013‑5880-5.
Avail­able at http://link.springer.com/article/10.1007/s11434-013‑5880-5

Abstract. Dozens of human cases infected with H7N9 sub­type avian influenza virus (AIV) have been con­firmed in China since March, 2013. Dis­tri­b­u­tion data of sexes, ages, pro­fes­sions and regions of the cases were ana­lyzed in this report. The results showed that the elderly cases, espe­cially the male elderly, were sig­nif­i­cantly more than expected, which is dif­fer­ent from human cases of H5N1 avian influenza and human cases of the pan­demic H1N1 influenza. The out­break was rated as a Grade III (severe) out­break, and it would evolve into a Grade IV (very severe) out­break soon, using a method reported pre­vi­ously. The H7N9 AIV will prob­a­bly cir­cu­late in humans, birds and pigs for years. More­over, with the dri­ving force of nat­ural selec­tion, the virus will prob­a­bly evolve into highly path­o­genic AIV in birds, and into a deadly pan­demic influenza virus in humans. There­fore, the H7N9 out­break has been assumed severe, and it is likely to become very or extremely severe in the future, high­light­ing the emer­gent need of force­ful sci­en­tific mea­sures to elim­i­nate any infected ani­mal flocks. We also described two pos­si­ble mild sce­nar­ios of the future evo­lu­tion of the outbreak.

Nishiura H, Mizu­moto K, Ejima K. The­o­ret­i­cal Biol­ogy and Med­ical Mod­el­ling. 4 May 2013. 10:30. doi:10.1186/1742–4682-10–30.
Avail­able at http://www.tbiomed.com/content/10/1/30/abstract

Back­ground. As the human infec­tions with novel influenza A(H7N9) virus have been reported from sev­eral dif­fer­ent provinces in China, the pan­demic poten­tial of the virus has been ques­tioned. The pres­ence of human-to-human trans­mis­sion has not been demon­strated, but the absence of demon­stra­tion does not guar­an­tee that there is no such transmission.

Meth­ods. A math­e­mat­i­cal model of clus­ter size dis­tri­b­u­tion is devised with­out impos­ing an assump­tion of sub­crit­i­cal­ity of the repro­duc­tion num­ber and account­ing for right cen­sor­ing of new clus­ters. The pro­por­tion of cases with a his­tory of bird con­tact is ana­lyt­i­cally derived, per­mit­ting us to fit the model to the observed data of con­firmed cases. Using con­tact his­tory with bird among con­firmed cases (n = 129), we esti­mate the repro­duc­tion num­ber of the novel influenza A(H7N9) from human to human.

Results. Analysing twenty con­firmed cases with known expo­sure, the repro­duc­tion num­ber for human-to-human trans­mis­sion was esti­mated at 0.28 (95% CI: 0.11, 0.45). Sen­si­tiv­ity analy­sis indi­cated that the repro­duc­tion num­ber is sub­stan­tially below unity.

Con­clu­sions. It is unlikely to observe an imme­di­ate pan­demic of novel influenza A(H7N9) virus with human to human trans­mis­sion. Con­tin­ued mon­i­tor­ing of cases and ani­mals would be the key to elu­ci­date addi­tional epi­demi­o­log­i­cal char­ac­ter­is­tics of the virus.