NEW YORK (Reuters) - The widening circle of people potentially exposed to Ebola in the United States is calling into question how well Dr. Thomas Frieden, the lead U.S. public health advisor, has communicated the risks of the deadly virus, according to crisis management and infectious disease experts.

When the first diagnosis of Ebola on U.S. soil was confirmed on Sept. 30, Frieden, director of the U.S. Centers for Disease Control and Prevention (CDC), clearly stated that additional cases were possible among contacts of the patient, Liberian Thomas Eric Duncan. Two nurses who cared for Duncan in Dallas have since been diagnosed with the disease.

But missteps by the CDC and Texas health officials that may have put the nurses and their contacts at risk, and Frieden's assurances that the situation was under control, have undermined public trust and fostered panic instead of confidence, critics said.

Until recently, the CDC enjoyed a stellar international reputation for handling public health crises such as the swine flu pandemic of 2009. But its standing was diminished after disclosures in June and July that scientists had mishandled samples of anthrax bacteria and avian flu virus at CDC headquarters in Atlanta.

Now, its handling of Ebola cases in the United States has put the agency under additional scrutiny.

Jonathan Bernstein, president of Monrovia, California-based Bernstein Crisis Management, said Frieden was "failing to control the fear" among the general public.

The CDC has said it has done its best to make agency leaders available to answer questions from the public and media about Ebola.

"We believe that we have an obligation to share information when we have it and recognize the changing nature of the ongoing response," said the agency's spokeswoman Barbara Reynolds.

"We balance the need to share information quickly with the desire of many to eliminate uncertainty," she said. "Without question communicating plainly and completely at the same time is always a challenge, but particularly so when people are confronted with a new risk such as Ebola."

HOLLOW PROMISES

Among the statements with which critics take issue are Frieden's repeated assurances that any U.S. hospital with an isolation ward could handle Ebola. Those have rung hollow after nurses Nina Pham and Amber Vinson fell ill while caring for Duncan.

The two were moved this week from Texas Health Presbyterian Hospital, where they worked and where Duncan was treated, to medical centers with special biocontainment units.

Daniel Diekema, an infectious disease specialist at the University of Iowa and president of the Society for Healthcare Epidemiology of America, said Frieden’s early assurances had led many hospitals to become complacent and think they did not need an Ebola plan. "I would venture to say most hospitals are not prepared," said Diekema.

Concerns over the CDC's Ebola response increased this week when Vinson traveled by plane with an elevated temperature, a symptom of Ebola, potentially exposing scores of travelers to the disease. Shortly after Frieden insisted on national television that Vinson should never have been allowed to fly, it emerged that she had consulted a CDC official about her slight fever before boarding the plane and received an all-clear.

Other experts point to statements from Frieden that go beyond scientific knowledge about Ebola. For instance, when he addressed concerns that the virus could be transmitted on buses and other public places, he stressed that patients with symptoms, who are contagious, would probably feel so sick they would stay home.

"That is not true for a significant number of Ebola patients early in their illness," said Brooklyn-based risk communications consultant Peter Sandman. "Ebola-infected healthcare workers (in Africa) have even gone to work in the early phase.”

“Most of the CDC director's statements go beyond available scientific data and … several are inconsistent with available scientific data,” said biosafety expert Richard Ebright of Rutgers University, a critic of the agency over its anthrax and avian flu accidents. He said the public must be aware by now that one day's statements are proven false by the next day's events.

A growing lack of trust over the country's official Ebola response has influenced actions by local authorities.

The Louisiana state attorney general obtained a temporary restraining order to prevent incinerated waste from the apartment where Duncan stayed from being buried in a Louisiana landfill, even though the CDC said the ashes posed no risk. Ohio and Texas closed some schools for cleaning out of concern over Ebola exposure, even though the risk of contamination was near zero.

Many U.S. lawmakers are demanding that the government ban travel from Guinea, Liberia and Sierra Leone, the countries hardest hit by Ebola, despite Frieden's argument that a ban would undermine efforts to contain the West African outbreak.

Perhaps the most confusing official messages concern when someone is infectious. Citing studies of outbreaks going back to 1976, the CDC has said that only when people show symptoms of Ebola, notably fever, vomiting and diarrhea, can they transmit the hemorrhagic virus, which is spread through contact with bodily fluids.

Four of Duncan's relatives were quarantined in Texas for 21 days, the longest period the virus is known to incubate, despite being asymptomatic. Several others, such as NBC correspondent Nancy Snyderman, who may have been exposed to an Ebola patient, have also been quarantined.

"It's another mixed message that makes people think officials are probably overconfident in saying you can only transmit the disease when you're symptomatic," said Jody Lanard, an independent risk communication expert in Brooklyn, N.Y.

(Reporting by Sharon Begley; Editing by Michele Gershberg, Toni; Reinhold)