( CNN ) -- A third case of Middle East Respiratory Syndrome in the United States has been reported . An unidentified Illinois man was infected after having `` extended face-to-face contact '' with an Indiana man who was diagnosed with the MERS virus . Fortunately , he is no longer ill . The rise in the reported number of MERS cases in the United States , Asia and Europe has fueled concern that this may be the big one : the 21st century equivalent of the 1918 influenza pandemic that killed 3 % to 5 % of the world population . Concern is appropriate , because the coronavirus responsible for MERS can evolve to become more potent public health threats . However , I do n't yet see evidence that will happen . For one thing , an increase in the number of reported cases is not equivalent to an increase in the number of actual cases . As MERS testing is expanded from people with severe disease to include those with mild disease or only a history of potential exposure , we will detect more cases of infection . The mortality rate associated with infection will decrease from the current estimate of 30 % . In short , we do n't yet know the extent to which an increase in the reported number of cases only reflects better case ascertainment . MERS , like 70 % of all emerging infectious diseases , including influenza , SARS , HIV/AIDS and ebola , originates in wildlife . With MERS , both bats and camels may be implicated . Studies of camels in Saudi Arabia indicate that the majority have a history of MERS coronavirus infection . Infection appears to occur in early life and then clears . Up to a third of young camels carry this infectious virus . Because camels are born in the spring , there may be an increased amount of virus circulating in camels in spring and summer months . This may contribute to a seasonal spike in the reported number of MERS cases . Humans may become infected through contact with infected animals , meat or other animal products such as milk . However , pandemic spread can not occur without efficient human-to-human transmission . The MERS coronavirus grows deep in the human respiratory tract , so it is less likely to be transmitted than viruses that grow in teh nose , mouth or upper airways where a sneeze or a cough is sufficient to create an infectious aerosol . Hospitalized patients with pneumonia-like MERS receive vigorous respiratory interventions such as intubation , assisted ventilation , drugs that dilate airways and chest percussion . These interventions may bring virus into the environment in aerosols and on the surfaces of medical equipment , resulting in infection of hospital personnel and other patients . Since the MERS coronavirus has been shown to be stable for up to 48 hours , it may be difficult to determine the source of infection as people and equipment circulate in the health care environment . To date , cases of human-to-human transmission have only been reported in hospitals and in families where there is intimate contact with an infected person . If we notice a change in this pattern such that clusters of infections begin to appear in communities with more casual contact , that would be a strong sign that the virus is evolving to become a pandemic threat . The MERS cases in new countries are disturbing but not surprising given how globally connected we are . International travel and foot traffic make it easier to spread a virus . The first two cases reported in the United States , in Indiana and Florida , were health care workers returning from Saudi Arabia . Although a third case has been linked to contact with the Indiana case , I am cautiously optimistic that a cluster of cases will not be triggered . Nonetheless , vigilance is essential . Saudi Arabia has more than 7 million foreign workers and hosts more than 3 million religious pilgrims annually . If new cases arise they will almost certainly be imported . The key to an effective pandemic response is to acknowledge that infectious disease challenges are global rather than national . Information and biological samples must be shared freely to facilitate surveillance and the development of diagnostics , drugs and vaccines . In this spirit , the government of Saudi Arabia has recently invited teams of international experts to join forces in addressing the global challenge of MERS . Although we are focusing on MERS now , the reality is that viruses and antibiotic resistant bacteria with pandemic potential are continuously emerging and re-emerging worldwide . The recent MERS cases should not trigger an alarm . But if a pandemic happens , it is important we are prepared to combat it .
A third case of Middle East Respiratory Syndrome in the U.S. has been reported . W. Ian Smith : The recent rise of MERS cases should not cause panic . He says if we see hundreds of cases that would be cause for concern . Lipkin : New MERS cases are not surprising given how globally connected we are .