Thanks to miles of centuries old sewage infrastructure, population density, improperly disposed food refuse and an emphasis on poisoning over prevention, Downtown Boston is home to more rats than anywhere else in the city.

A recent report, the Boston Rodent Action Plan (BRAP), identified Downtown as one of four Priority Action Neighborhoods (PAN) where rat infestations require significant attention. Chinatown, Downtown, the North End and Haymarket collectively ranked highest on the BRAP scale of severity, where formal complaints were made for 1 in every 41 residents, according to 311 data. After Allston/Brighton, the Back Bay/Beacon Hill area ranked third, where complaints were made for 1 in every 77 residents.

The BRAP acknowledges that there can be significant bias present in 311 data, including repeated complaints from vocal community anti-rat groups.

In addition to 311 data, to determine PAN the BRAP used violation data from the Inspection Services Department and two days of targeted field surveying with a consulting rodent scientist.

The Boston Public Health Commission says that rats do not currently pose a high public health threat to Bostonians.

In a statement made over email, urban rodentologist Dr. Robert Corrigan said that Downtown, Chinatown, North End and Haymarket showed signs of the most severe infestations, but there was no statistically significant difference in the rodent presence between downtown neighborhoods.

The number one driver of rat populations is food refuse, and open-air markets, abundant restaurants and aging infrastructure make downtown the perfect environment for rodent populations to thrive. A single reliable food source, such as food shrapnel from litter or markets, improperly used dumpsters, plastic garbage bags and cheap trash cans, can sustain hundreds of rats that will spill over into adjacent areas.

The Norway rat, Boston’s only urban rat species, is capable of chewing through the most commonly used cheap plastic trash can in under an hour. Food refuse left out in plastic bags doesn’t stand a chance.

“Complete removal of all food garbage from the site before nightfall and cleaning after each market day are critical to preventing very serious rat infestations,” reads the BRAP. “ In downtown, it’s not simply enough that the front of the house be clean.”

Even if the streets and storefronts of downtown restaurants appear sanitary and free of refuse, the numerous well-shaded alleyways of downtown, where garbage is disposed of, provide plenty of food and shelter. The majority of doors examined during the BRAP field survey were found not to contain any rodent proofing at all.

The report recommends a refuse inspection pilot, increased enforcement of proper refuse disposal in residential and commercial areas of downtown and daily emptying of pedestrian litter receptacles on public streets and parks prior to nightfall.

Public parks like the Boston Commons and Public Gardens are another source of food, and thus infestations. In addition to natural food sources like worms, grubs and bird eggs, the presence of shrubbery and fresh water make for cozy nesting grounds. Because removing green space and gardens is antithetical to the BRAP mission of making parks more enjoyable, the report suggests increased monitoring of likely hot spots through remote sensors to ensure swift action prevents colonies from taking root. Such sensors are also suggested for placement at Fenway Park.

The BRAP recommendations reflect an emphasis on prevention, rather than the typically reactive responses of property owners.

“Rat poison bait boxes were found to be overly abundant in locations and in numbers per location, to the point of nonsensical and in some areas also not in adherence EPA pesticide label laws, in virtually all the neighborhoods visited,” reads the BRAP. Boston’s miles of old brick sewers are a sprawling home to centuries-old rat colonies that will happily replace exterminated surface rats so long as food refuse remains accessible.

Additionally, the over-application of poison actually kills the rats’ natural predators. Once consumed, it can take a week for the rodent to actually die, during which time they become more sluggish and the easiest targets for predators who then ingest the poison in the rodent’s body.

For this reason, the BRAP suggests a pest management approach that is 80% addressing environmental root causes, such as food refuse, rodent-proofing and surveillance, and 20% last-resort extermination.