SARS-CoV may follow the path of influenza

ATLANTA — While stringent infection control procedures in communities and hospitals around the world seem to have stunted the epidemic of severe acute respiratory syndrome associated coronavirus (SARS-CoV), some health officials fear the disease might simply be following the cyclic pattern of its virus family — a path that mirrors the cold and flu season.

“The bottom line is we don’t know,” said Julie L. Gerberding MD, MPH, director of the CDC. “This is a respiratory illness. Most respiratory illnesses are worse in the winter months and improve or disappear in the summer months, but it’s anybody’s guess what will happen in the fall.”

The threat

The microbial health threat known as SARS-CoV has been responsible for more than 8,000 cases and the deaths of more than 700 people globally. It is the newest member of the corona family of viruses, a family so named because of its signature characteristic — an outer envelope that contains clubbed shaped projections that radiate, which provide the appearance of coronas or halos when the virus is viewed under a microscope. These spikes “bind to receptors on the host cells and fuse the viral envelope with host cell membranes,” a study in The New England Journal of Medicine noted.

Formerly responsible for about 30% of the world’s common colds, this genus of pleomorphic viruses caused mild upper respiratory infections before SARS. Rarely did they cause lower respiratory tract disease in humans. “In contrast, coronaviruses cause devastating epizootics of respiratory or enteric disease in livestock and poultry,” the study said.

The study supposes that because it had never before been seen among humans, the new coronavirus is “probably from a non-human host that somehow acquired the ability to infect humans.”

Gerberding echoed this sentiment when she said, “I think what we’re seeing here is a situation that is most explainable by natural evolution of coronaviruses, either from an animal or a poultry source, or possibly a coronavirus that’s evolved in a human.”

The mortality rate for SARS-CoV has hovered around 8%, but could easily rise to 15% or even 20% if the disease becomes endemic. “People with underlying illness seem to be predisposed to more severe disease, and this may be due to a compromise of the immune system,” John Jernigan, MD, MS, co-leader of the Clinical and Infection Control SARS Investigation Team of the NCID and CDC told Infectious Disease News. “Diabetes mellitus seems to be a common theme. Six of the eight deaths that were reported in JAMA by the Canadian group had diabetes mellitus. We have heard similar themes in Hong Kong, but that is by no means the only disease associated with this [mortality rate for the infirm].”

Jernigan also expressed concern that SARS-CoV will not simply disappear if containment is successful. “We are concerned that SARS is here to stay. Other human coronaviruses do have seasonality to them. It is encouraging that we are seeing some decreases in the number of cases in several areas around the world, with some exceptions.”

Jernigan said vigilance is important for the future. “I think we need to be cautious about this. We may be looking at a second wave in the upcoming viral respiratory season. We need to be prepared to deal with that if it should occur.”

During a CDC telebriefing, Gerberding affirmed that the CDC is in fact preparing for the virus’s return.

“We need to be prepared for the possibility that we’ll see a resurgence or even expansion of SARS next fall … We are currently in the process of developing a contingency plan for the potential for a resurgence or an expansion. I think that’s a prudent measure, I pray we don’t need it, but we want to be ready and we’ll be ready if we have to go there.”

SARS plus influenza: one-two punch

The world has been lucky that the spread was not worse. It could be, if SARS-CoV returns in the autumn with the cold and flu season and gains a foothold again anywhere in the world. According to the CDC Web site, it is estimated that about 10% to 20% of U.S. residents get influenza, and an average of 114,000 people are hospitalized for influenza-related complications. Thirty-six thousand Americans die on average per year from the complications of influenza. In fact, together influenza and respiratory syncytial virus are the leading causes of death from respiratory illness in those aged 65 years and older. If a drug, vaccine or some sort of solution is not devised and SARS-CoV returns in a second wave, as Jernigan said may very well happen, the effects on the elderly, the immunocompromised, others living with chronic conditions and even the mildly ill could be devastating.

“This is a sobering situation for everyone, and as we have been saying from the beginning, SARS is a problem for everyone — not just the people of Asia,” Gerberding said.

For more information:

• CDC. Cluster of severe acute respiratory syndrome cases among protected health-care workers — Toronto, Canada, April 2003. MMWR. 2003;52(19):432-436.
• Holmes K. SARS-associated coronavirus. N Engl J Med. 2003;348(20):1948-1951.