The coronavirus has swept at varying speeds across Long Island communities that stretch from the New York City line to the tips of the north and south forks, according to a Newsday analysis of data from New York State and Nassau and Suffolk counties.

The counties are tallying confirmed cases of the virus as they show up in the Island’s towns, villages and hamlets, with clusters of higher cases influenced by factors including compliance with social distancing, population density and the level at which residents have been tested for the virus.

Mapping the number of known cases provides a snapshot of where the virus has emerged at a moment in time without offering explanations as to why some localities have higher numbers of cases than others. Those answers would only come with detailed epidemiological studies.

The tallies by the two counties were released Friday. They, of course, do not include infections that have not been detected by testing and are expected to change dramatically as the virus continues its march.

Health experts warned that residents of areas with comparatively low infection counts should adhere to strictly limiting social contacts, handwashing and avoiding touching their faces.

“Everybody should assume that anybody around them, anybody that doesn't live in their household, can give it to them,” said Dr. Bettina Fries, chief of the Division of Infectious Diseases at Stony Brook University. She said tracking individual cases will slow as health officials focus on getting people to stay home as much as possible to prevent the spread.

As of Friday, the counts per community differed widely.

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They ranged in Nassau, for example, from one reported case in Cove Neck, a low-density hamlet on Nassau’s northeast border, to 189 in Woodmere, a higher-density community at the county’s southwest nub.

In Suffolk, the health department reported a single case in each of 18 communities, including Flanders, Montauk and Great River. At the other end of the scale higher-density Huntington Station was listed with 178 cases.

Varying rates of testing make comparisons difficult.

For instance, based on information released Saturday, Nassau County's rate of confirmed cases (408 per 100,000 residents), is 16% higher than New York City's rate (353 per 100,000 residents).

However, Nassau's rate of testing is 35% higher than that of New York City, while its death and hospitalizations rates are lower than the city's.

Suffolk has counted 278 cases per 100,000 residents. Its rate of deaths was the same as Nassau County’s and its hospitalizations rate was less than half.

On average, Long Island’s communities have experienced 21 confirmed cases. The median number is nine, meaning that half of the communities have counted more than nine and half less than nine.

Confirmed case rates differ widely among communities and require context.

In the Town of Southold, home to the North Fork’s vineyard country, an early outbreak drove the frequency of infections to 592 cases per 100,000 people, according data released Saturday. That is the highest rate among Suffolk towns and is higher even than the rate reported in Wuhan, China, where the pandemic was born.

Even so, the number of cases in Southold with a comparatively sparse population has been counted at 129 — less than the number tallied in the highest ranked communities of Huntington Station (178), Brentwood (152) and Huntington (139).

In Nassau County, Woodmere has suffered both the highest number of cases and the highest per capita rate of cases among the county’s villages and hamlets.

Woodmere is home to a substantial Jewish population, whose members gather for prayer services, holidays, Shabbat dinners, and pack bar and bat mitzvah celebrations and weddings. The Jewish holiday of Purim, which fell on March 9, came before Gov. Andrew M. Cuomo imposed restrictions on the size of crowds.

Fourteen rabbis in the Woodmere area wrote a letter on March 13, immediately suspending services and other religious gatherings.

Rabbi Noam Weinberg, a volunteer emergency medical technician with the Woodmere Fire Department, and principal of North Shore Hebrew Academy High School in Great Neck, said the spread of the virus could have happened before the restrictions took effect.

Rabbi Hershel Billet, who leads Young Israel of Woodmere, said some of the local synagogues held services during the weekend of March 13 and 14, which “may have inadvertently” led to the spread of the virus among the congregants of those synagogues. He stressed that “the Jewish community is not guilty of anything here.”

“I can tell you that the official rabbinical response was that every temple should close down,” said Dr. Aaron Glatt, assistant Rabbi of Young Israel of Woodmere. He is also chair of medicine and chief of infectious diseases at Mount Sinai South Nassau Hospital in Oceanside.

General social activity before the state shutdown may have spread the virus, experts said.

Even the unlucky timing of Huntington’s St. Patrick’s Day Parade, held March 8 — a week before most festivities were canceled — could have been a contributing factor in the high number of cases in Huntington and Huntington Station, according to Suffolk Legis. Dr. William Spencer (D-Centerport), a former president of the Suffolk County Medical Association.

He cited as other possible factors: greater access to testing, denser housing and struggles in reaching Spanish speakers in the community.

In an interview, Nassau Health Commissioner Lawrence Eisenstein attributed higher counts to causes including housing density, whether residents commuted into New York City, or work on the front lines against the outbreak — as medical providers, first responders or supermarket workers.

“We look at New York City's experience and we know that population density seems to be a greater risk factor,” Eisenstein said.

Hempstead in Nassau and Brentwood in Suffolk both have comparatively high population densities and high case numbers: Hempstead (162) and Brentwood (152).

“There are more apartment buildings in that area than in the entire county,” said Nassau County Legis. Kevan Abrahams (D-Freeport), who represents Hempstead.

“It’s very hard to avoid other people and maintain social distancing especially because people need to get out to do their grocery shopping.”

Testing has also ramped up in Hempstead, which contributes to the higher numbers, he said.

State Sen. Monica Martinez (D-Brentwood) pointed both at density and at the fact that many residents there are deemed essential workers and can’t stay home and isolate.

“I know many members of Brentwood, Bay Shore and Central Islip are on the frontlines as first responders,” Martinez said in a text message. “I believe it’s a testament to the hardworking people of these communities who like many other working-class neighborhoods have to face the dangers of reporting to work because they’ve been deemed essential.”

With Candice Ferrette