SARS spread from live markets, but when?

From ANIMAL PEOPLE, October 2003:

BEIJING–Blood tests indicate that about 1% of the children
in 17 provinces of China were exposed to Severe Acute Respiratory
Syndrome before the outbreaks of 2002-2003 that hit 24 of the 31
provinces.
Evidently passing from animals sold in filthy live markets to
humans working in food preparation, and then spreading from human to
human, SARS eventually killed 916 people in 32 nations, with about
650 of the deaths occurring in mainland China and Hong Kong.
The blood study was conducted by the Beijing Military Zone
Air Force Logistics Sanitation Unit, using samples taken from
healthy children before SARS appeared.
In a parallel study, the Beijing Capitol Pediatrics Research
Institute found that among 77 children hospitalized for various
reasons in 2001, 42% had antibodies to SARS. Among 92 children
hospitalized during the SARS outbreak, 40% had the antibodies–but
none had SARS symptoms.
Both studies indicate that the coronavirus responsible for
SARS was already widely distributed among the human population–at
least among children–well before it turned deadly. The findings may
explain why relatively few children developed the deadly strain of
SARS, but confounds the mystery of how SARS originated, since
children are also less likely than adults to consume wildlife
products.

One possibility is that children receive antibodies to SARS
via mothers’ milk. Chinese women may be more likely than men to be
exposed to SARS through food preparation and tending farmed wildlife,
but men are the major wildlife eaters.
A Beijing University Hospital study meanwhile confirmed that
SARS is not easily transmitted to people who take precautions against
the it, finding no evidence that SARS ever passed from patients to
the health workers who treated them.
The three new studies by Beijing institutions were released
three weeks after Hong Kong University gene sequencing expert Guan Yi
and team reported in Science that they discovered antibodies 99.8%
identical to the SARS-like virus antibodies found in four masked palm
civets and a raccoon dog last May in eight of 20 wildlife traders,
three of 15 slaughterers, and one of 20 vegetable sellers tested at
the Guangdong market where the exposed animals were found.
None of the market workers actually had SARS.
“Our investigation clearly shows that the SARS-like virus
comes from the SARS-like virus in the wild animal market,” Guan Yi
said. “But we still have no direct evidence that the viruses in the
markets can attack humans directly.”
Harvard Medical School scientific reviewer Henry Niman, MD., told
Mary Ann Benitez of the South China Morning Post that the Guan Yi
team also found a direct link between a masked palm civet and two
infected Guangdong health workers.
In mid-August 2003, four months after suspending wildlife
sales, the China State Forestry Administration reauthorized the sale
of 54 species of wildlife as live meat or pets, providing that the
animals are captive-raised.
“Lifting the ban was a bit reckless,” Niman said.
Maria Cheng, spokesperson for the Beijing office of the
World Health Organization, agreed with Niman that, “Perhaps it
would have been better to wait until we had more information for
China to lift the ban” on wildlife consumption.
Hong Kong legislator for the medical sector Lo Wing-lok and
legislator for food and hygiene Fred Li Wah-ming called for the ban
to be reimposed.
Wary of protests that broke out in Guangdong in early summer,
however, led by unemployed wildlife traders, an anonymous mainland
State Forestry Administration official reportedly dismissed the new
findings as inconclusive.
French epidemiologist Francois Moutou told Agence France-Presse in
August that a 14-member team of United Nations and Chinese experts
had found SARS-like viruses in a wide range of birds, reptiles, and
mammals at markets and farms in south China. Their conclusions,
however, have not yet been scientifically reported.