If you plan to garden this weekend, be sure to wash your hands afterwards. Research shows that activities involving exposure to compost can increase the risk of contracting Legionnaires’ disease.

Inhaling or ingesting compost may increase the risk of legionellosis

Legionnaires’ disease is a form of pneumonia most commonly caused by the bacteria Legionella pneumophila, which is found in lakes, streams, and other freshwater terrain. Legionnaires’ disease is contracted by inhaling small droplets of water contaminated with L. pneumophila. This can happen, for example, when taking a shower using a water system in which the bacteria has grown and multiplied. While the majority of people do not get sick from Legionella bacteria, certain groups are more susceptible. These include the elderly, smokers and people with chronic lung disease.

A lesser known cause of Legionnaires’ disease is a bacteria called Legionella longbeachae.

First isolated in 1980 from a patient in Long Beach (California), L. longbeachae is found in compost and potting soil. Studies have suggested that inhaling and ingesting these products can cause Legionnaires’ disease. A researcher from New Zealand and her colleagues sought to determine the main risk factors for infection with L. longbeachae. The researchers recently published their findings in Emerging Infectious Diseases.

Gardeners need to be careful

The study involved 31 adults who had been hospitalized with L. longbeachae-related legionellosis, as well as 172 controls. Over two summers, participants completed questionnaires detailing their demographics, smoking habits, pre-existing health conditions, and any activities that may have exposed them to compost or potting soil, such as gardening.

The study suggests that gardening is an important risk factor for legionellosis. Almost all patients with the disease reported having done some gardening in the three weeks before their illness, which brought them into contact with purchased compost products. Washing hands immediately after contact with compost products was associated with a lower risk of legionellosis, although wearing masks or gloves did not appear to help reduce the risk.

Other risk factors for Legionnaires’ disease included smoking and a diagnosis of chronic obstructive pulmonary disease. Based on their findings, the researchers say gardeners should be careful when handling compost products.

The researchers recommend that gardeners avoid inhaling compost or potting soil, by opening the bags away from the face and keeping them close to the ground when moving them. In addition, always wash your hands with compost and potting soil before bringing them close to your face.

Smokers and people with chronic obstructive pulmonary disease should pay particular attention to these safety measures when gardening.

Why compost is very useful in more ways than one

The health risk we’ve discussed shouldn’t deter you from creating and nurturing a compost; it is very helpful. Many people decide to compost for environmental and personal health reasons. Composting helps reduce waste in landfills. Rather than throwing certain food or yard waste in the trash, a person can compost it. This allows this waste to naturally return to the earth and reduces the amount of waste in landfills. It can also help a person save money on waste collection costs.

Using compost, humus or mulch in gardens improves the nutrient content of the soil.


Reduces methane, a greenhouse gas from landfills.
Reduces or eliminates the need for chemical fertilizers.
Promotes higher crop yield for farmers.
Helps restore forests, wetlands and habitats by improving poor quality soils.
Helps soil recover from hazardous waste contamination.
Allows the soil to retain its moisture level, reducing the need for watering.
Reduces the amount of carbon dioxide in the atmosphere.
Since compost can improve soil health and reduce greenhouse gases, it can have beneficial effects on human health.

Compost is made up of four ingredients:

green matter (rich in nitrogen)
brown matter (rich in carbon)
moisture (water)
oxygen (air)
Together, these ingredients create an environment that allows bacteria, fungi, worms and other organisms to naturally break down organic matter into compost.

Green materials

Green materials include nitrogen-rich organic materials, which provide amino acids and proteins to the compost. Green materials include:

fruit and vegetable scraps, peels, cores and seeds
coffee grounds and coffee filters
manure from herbivores, such as cows, sheep, and goats
bread, cereals
cooked rice and pasta
herbs and spices
nuts and nut shells
crushed eggshells (no egg white or yolk)

Brown materials

Brown materials are carbon-rich materials. She understands:

dead leaves
hay and straw
tree branches and twigs
the box
wood chips and sawdust
fireplace ashes
shredded newspapers
flower clippings
indoor plants
loose leaf tea and natural tea bags
cotton fabric drying lint

What not to compost

An easy way to remember what to compost is to think about where the material came from.

Foods and other products that come from the ground are generally safe to compost. These include fruits, vegetables and grains, as well as their remains and seeds.
Products that do not come from the ground cannot be safely composted. These include animal products, products from unnatural sources, or oily foods.

Also, some things can disrupt the composting process or introduce disease. Do not compost:

animal meat, bones, fat and skin
yogurt, milk, cheese, butter and other dairy products
egg yolks and egg whites
manure from pets and meat-eating animals, such as dogs and cats
fatty foods or oils
sawdust or pieces of treated wood
Onions and garlic can repel earthworms. This is why many people do not add them to their compost.

* criptom strives to transmit health knowledge in a language accessible to all. In NO CASE, the information given can not replace the opinion of a health professional.