in february 2013 , a novel avian influenza a ( h7n9)virus emerged in eastern of china and quickly spread to other areas. up to may 2 , 128 human infections have been confirmed , with 26 deaths . transmission may occur through direct or close contact or through exposure to environments that are contaminated with infected poultry . even though no human - to - human transmission has been reported , it raises serious concerns for public health . influenza a viruses , belonging to the family orthomyxoviridae and possessing 8 negative - sense rna segments encoding 11 known proteins , are divided into subtypes , based on the nature of their surface glycoproteins , hemagglutinin ( ha ) and neuraminidase ( na ) . currently , 16 ha and 9 na subtypes have been identified in wild water birds , the natural host for all influenza a viruses and the reservoir from which viruses emerge to infect domestic poultry and occasionally mammals . only some of these subtypes have been identified in humans , specifically the h1n1 , h2n2 , and h3n2 viruses , corresponding to the three major pandemics of the last century . influenza a viruses are known to also infect a variety of other mammals , including pigs , horses , mink , felids , and so on . influenza a viruses infecting poultry can be divided into two distinct groups on the basis of their ability to cause disease in chickens . the very virulent viruses cause highly pathogenic avian influenza [ hpai ] , in which mortality may be as high as 100% . these viruses have been restricted to subtypes h5 and h7 ( e.g. h5n1and h7n7 ) , although not all viruses of these subtypes cause hpai . all other viruses cause a much milder , primarily respiratory disease designated low pathogenicity avian influenza [ lpai ] . due to its rapid spread and high mortality , hpai is classified as a list a disease by the world organization for animal health ( oie ) and type a disease by the chinese ministry of agriculture , respectively . in recent years , several avian influenza outbreaks caused by the h7 subtypes in poultry were reported in such countries as the usa , north korea , south korea , bulgaria , japan , denmark , germany , and the netherlands. in march and april 1997 , there were outbreaks of h5n1 avian influenza in hong kong , . due to host restriction , avian influenza a viruses are generally difficult to cross the species barrier and are not efficiently transmitted among humans . according to the current literature available , most of human infections with avian influenza h7 is the most common pathogen of human infection , and human infections with avian h7 subtype virus ( e.g. , h7n2 , h7n3 , and h7n7 ) have been reported occasionally in north america and europe in recent years . the first reported case of direct transmission of a sub - type h7 virus from an avian to a human host occurred in 1996 , when conjunctivitis developed in a woman who kept pet ducks 1 day after she experienced a possible eye abrasion while cleaning her duck house , . an outbreak of subtype h7 infections in humans occurred in the spring of 2003 , when an hpai ( h7n7 ) virus was detected in commercial poultry farms in the netherlands and necessitated the culling of > 30 million birds , . eighty - six persons involved in the culling operation and 3 of their family members who had not been in contact with infected poultry had virologically confirmed subtype h7 illness , which suggests that limited human - to - human transmission of the avian virus also had occurred . most recently , multiple h7 viruses have resulted in human infections in the united kingdom . in 2006 , an lpai virus ( h7n3 ) was isolated from a poultry worker with conjunctivitis . in 2007 , h7n9 virus discovered in february 2013 in china is a novel avian influenza a virus , which has not been detected in humans or animals previously and is prevalent and causing an emerging fatal infectious disease in several provinces in china now . this human h7n9 virus is the product of reassortment of viruses that are of avian origin only , with the ha genes and na genes from h7 and n9 subtypes , respectively , and 6 internal genes from the h9n2 subtype . to date , a total of 128 laboratory - confirmed cases of human infection with avian influenza a(h7n9 ) virus including 26 deaths have been reported to the who , which are distributed in 39 cities of 10 provinces , such as zhejiang , shanghai , and jiangsu . in these reported cases , males were nearly two times more than females , and most of them were above 50 years of age . in jiangsu province , the onset of illness of the first confirmed case was on march 19 , 2013 . sporadic cases occurred in succession and 27 confirmed cases including 4 deaths had been accumulatively reported till may 2 , 2013 , just slightly lower than those reported for zhejiang province ( 46 cases , including 6 deaths ) and shanghai city ( 33 cases , including 13 deaths ) . the cases were concentrated in the southern regions of jiangsu province , 11 in the city of nanjing , 6 in suzhou and 4 in wuxi . in addition , changzhou , zhenjiang , yangzhou , xuzhou , suqian and yancheng had 1 case , respectively . the average age of the infected cases in jiangsu was 54.0 years , and the youngest and the oldest were 21 and 85 years old , respectively . there were 19 males and 8 females , and the male to female ratio was 2.38:1 . only five of these contacts developed fever , cough or sore throat , but were at last excluded from h7n9 infection by laboratory tests . the cases were concentrated in the southern regions of jiangsu province , 11 in the city of nanjing , 6 in suzhou and 4 in wuxi . in addition , changzhou , zhenjiang , yangzhou , xuzhou , suqian and yancheng had 1 case , respectively . the average age of the infected cases in jiangsu was 54.0 years , and the youngest and the oldest were 21 and 85 years old , respectively . there were 19 males and 8 females , and the male to female ratio was 2.38:1 . only five of these contacts developed fever , cough or sore throat , but were at last excluded from h7n9 infection by laboratory tests . according to the latest research results , the prevalence of human infection with the avian influenza a ( h7n9 ) virus has the following characteristics : base on the information available , so far it is still inferred that the source of human infection with avian influenza a ( h7n9 ) was originated from poultry . it means that the most important source of human infection would be exposure to environment contaminated by infected poultry or directly touching the infected poultry . in addition , trading of freshly slaughtered poultry in the wet markets in cities may be a confirmed risk factor to human infection . analysis of population distribution and medical history of the human cases indicated that human infection with h7n9 subtype virus mainly occurred in older people , or people with chronic diseases or who were immunocompromised . clinical studies suggested that most of the infected human cases presented acute onset and progressive deterioration . so far , there is no evidence of sustained human - to - human transmission . however , two confirmed cases have been associated with possible family cluster . at present , there is no evidence that the international animal trade or population flow would provoke a pandemic risk . however , due to the limited knowledge about the source of infection and the animal reservoirs , specific control and prevention measures can not be taken . therefore , it is foreseeable that the affected area would be further expanded in the recent future . in summary , it is impossible that a pandemic or outbreak of human infection with avian influenza a ( h7n9 ) virus will happen in jiangsu province in the near future . the cases of human infection with avian influenza a ( h7n9 ) virus should be timely detected , diagnosed and given proper treatment through the following prevention and control measures : strengthen the routine surveillance of influenza like illness ( ili ) and severe acute respiratory infection ( sari ) , and screening cases of human infection with avian influenza a(h7n9 ) virus ( especially clusters of such cases ) throughout the province . take full advantage of the  china infectious disease automated alert and response system ( cidars )  which will immediately send a warning message as soon as a confirmed case or a surveillance case of human infection with avian influenza a ( h7n9 ) virus was reported through the internet to the database of the infectious disease direct reporting system . once receiving such a message , the district cdc staff must carry out on - site verification within 2 hours . workers of all the medical institutions should enhance their sense of responsibility in the diagnosis and treatment of suspected cases of human infection with avian influenza a ( h7n9 ) virus . develop an integrated control and prevention system based on the coordination between different ministries , departments and agencies : the most important task is to treat patients and track close contacts to carry out medical observation conscientiously . hospitals with admitted patients should pay attention to self - protection of health workers and disinfection of the environment and isolation of cases or suspected cases so as to prevent the occurrence of nosocomial infections . the management of live and slaughtered poultry trade in wet markets should be enhanced and sick or dead birds or animals should be disposed properly . carry out a wide range of health education activities about human infection with avian influenza a ( h7n9 ) virus via the media , such as the internet , newspapers , and television , which may make the public understand this emerging disease correctly , reduce unnecessary worries about it , and most important of all , improve self - awareness of infection prevention . clinical researches and epidemical studies are urgently needed to understand this novel virus and the emerging disease caused by it : identify the source of human infections and the animal reservoirs of this novel virus . ascertain the mode of infection and the risk of human to human transmission . actively study the specific preventive vaccine and efficient drugs or therapies for this novel disease .
a novel avian influenza a ( h7n9 ) virus was discovered in february 2013 in china and has resulted in more than 100 comfirmed human infections including 26 fatal cases as of may 2 , 2013 . 
 the situation raises many urgent questions and global public health concerns . in this study , 
 epidemiologic characteristics of infected human cases in jiangsu province were analyzed and risk assessment was undertaken based on the information available . 
 briefly , it is highly unlikely that a pandemic of human infection with avian influenza a ( h7n9 ) virus will happen in jiangsu province in the near future . in the end , some measures are recommended to prevent the situation from becoming worse .