Tag Archives: Infection

Infection Is a Risk Factor for Cancer

We have discussed the association of salmonella typhi with gallbladder cancer in the last post. Let’s look at more examples on this topic.

Helicobacter pylori is linked to both gastric cancer and MALT lymphoma (a form of lymphoma involving the mucosa-associated lymphoid tissue, often in the stomach); Chlamydia pneumoniae to lung cancer; Streptococcus bovis and/or Enteroccocus faecalis to colon cancer.

Although research has shown that certain bacteria are associated with human cancers, their role in cancer is of complex. Convincing evidence links some species to the formation of cancer while others appear promising in the diagnosis, prevention or treatment of cancers. However, you might wonder how bacteria infection could lead to cancer. Here I provide you some insights.

Bacteria may cause cancer through:

1. Chronic infection. Some bacterial toxins can negatively impact the process that controls the normal cell cycle and cell growth, others disrupt the cellular signaling pathways that regulate normal cell death, consequently promoting cancerous growth. In addition, infection-induced immune response may release immune modulating substances from inflammatory cells, contributing to carcinogenesis.

2. DNA damage. Bacteria can produce free radicals – very unstable but highly reactive with other molecules. They can bind to DNA and cause DNA mutation, thereby altering the genes that control normal cell division and cell death. Cancer is initiated when uncontrolled growth of abnormal cells takes place.

3. Weakened or suppressed immune system. The immune system is an important line of defense for any toxins or diseases including cancer. Toxins or pathogens sometimes can get away from the host’s immune system to survive, and then modify one’s immune function. When its function is compromised, the immune system no longer recognizes and fights bacteria or toxins as foreign bodies, nor gets rid of them.

That being said, don’t panic. A majority of individuals will not develop cancer after infection by a cancer-causing agent. However, be conscious and alert. The facts are:

  1. Certain individuals are more susceptible to cancer-causing infections.
  2. Incidence of certain cancers may vary among populations or geographic regions.
  3. It often takes years or decades between acquiring the infection and getting cancer.


Chronic infection is a risk factor for cancer. Staying away from or treating the infection may prevent it.

Photo illustration: Color-enhanced scanning electron micrograph showing Salmonella typhimurium (red) invading cultured human cells

Photo credit: Rocky Mountain Laboratories, NIAID, NIH

Salmonella Infection — How to Avoid the Risk

Do you eat eggs? They are nutrient-rich, esp. vitamin D-rich food. Now you know eggs can also be a source of food poisoning, based on the fact that Salmonella outbreaks drove a nationwide egg recall recently. The New York Times reported that a half billion eggs have been recalled because of possible contamination with salmonella.

Today we focus on top 3 takeaways from this incident.

First, who is most vulnerable to salmonella infection?

Salmonella infections cause nausea, vomiting, diarrhea, and abdominal cramps, as well as fever. Usually symptoms of infection begin 12 to 72 hours after consuming contaminated foods/ beverages, and last 4 to 7 days. However, some cases can be serious and even fatal. In particular, the following populations are at high risk:

  • young children
  • elderly or frail individuals
  • people with compromised immune systems, such as cancer patients and those undergoing chemotherapy

Second, what precautions can you take to eliminate the risk of infection?

Again, the food safety system has failed to eliminate salmonella threat. Therefore, you need to take some precautions to protect yourself and your family from food poisoning or bacteria infection. Based on recommendations from the U.S. Centers for Disease Control and Prevention and my own practice, I’ve compiled the following eggs/poultry safety Dos and Don’ts.


The Don’t list:

  1. Don’t eat raw or undercooked eggs.
  2. Don’t use raw eggs for salad dressing or homemade ice cream.
  3. Don’t handle food, esp. cooked food or ready-to-eat food before washing your hands.
  4. Don’t consume unpasteurized milk or any raw dairy products.
  5. Don’t eat restaurant dishes made with raw or undercooked eggs.
  6. Don’t prepare food or serve food/drink for others when you’re infected by salmonella.

The Do list:

  1. Do wash your hands thoroughly after handling poultry and anytime before preparing foods, especially cooked or ready-to-eat items.
  2. Do thoroughly wash the cutting board, involved counter surface, knives, utensils and containers/plates after handling uncooked poultry or foods.
  3. Do separate the cutting board or plates for raw food from those for cooked or uncooked ready-to-eat food to avoid cross-contamination; — a practice that many folks overlook.
  4. Do throw away any cracked or dirty eggs.
  5. Do keep eggs or egg-containing foods refrigerated at 45oF or lower.
  6. Do cook eggs until they are well-done (i.e., both yolks and whites are firm).
  7. Do judge or determine whether meat or poultry is cooked or safe to eat by a food thermometer when in doubt, not by food color or poking depth.
  8. Do make sure to cook any egg mixture (casseroles or cakes/pies) until the center of the mixture reaches a safe temperature level.

Third, is Salmonella infection linked to cancer risks?

The relationship between bacterial infection and cancer is rather complicated in the way that bacteria can either cause one type of cancer or protect from the other type of cancer or both. Here we only look at the link between salmonella bacteria and cancer – it’s like two sides of a coin.

There is a close association between mixed bacterial and salmonella infections with the carcinogenesis of cancer, particularly gallbladder cancer – a cancer with a poor prognosis. Even though one infection won’t get you cancer, repeated bacterial infections or chronic infections may lead to cancer development. Therefore, don’t overlook infection. As WHO advocated, preventing infection is one strategy to prevent cancer.

Reversely, the same bacterium, salmonella, has been found as a potential strategy to fight melanoma – the deadliest form of skin cancer. Specifically, research showed that injecting salmonella (of course, in a safe form) into cancerous mice and cancer cells from human melanoma increased an immune-killing response to tumor cells through elevating immune surveillance.

In short, food hygiene and food safety measures are always worthwhile for your overall health.

Photo credits:  by andar; by g-point

The infection may be gone, but the risk may not.

My father had pulmonary tuberculosis nearly 4 decades ago. Clinically, it had been considered healed tuberculosis after timely treatment along with years of monitoring. Even until 2 years ago before diagnosis of lung cancer, the only thing showing on his chest X-ray was a localized calcification (i.e., calcium deposition, a mark of healed lesion in his case) without any visible changes. Also, he was symptomless concerning any upper-respiratory diseases. Unexpectedly, there were some lung malignancies clearly showing on his very last chest X-ray in 2009 — one that appeared significantly different compared with the one taken 2 years prior.

Virus_1259076_untitledThere are countless similar stories regarding the link between personal histories of infectious diseases and cancer. A friend of mine died of liver cancer in his 40s — a real tragedy given his age. It turned out that he had hepatitis (infected with hepatitis B virus) when he was young.

It’s scientifically proven with regards to infection-associated cancer. Pancreatic inflammation appears to increase the risk of pancreatic cancer, and some patients with pancreatic cancer had history of pancreatitis. A history of urinary tract infection is currently accepted as a risk factor for developing bladder cancer, and has been positively linked to the development of renal cell carcinoma (kidney cancer), with notably elevated risks for men with a history of smoking.

An infective agent is linked to some of the most common cancers. Human papilloma virus (HPV, also called “wart virus”) is responsible for cervical cancer, one of the most common cancers affecting women. A two-fold danger exists with this disease. First, HPV is highly transmissible and considered the most common sexually transmitted infection in most populations; second, most women infected with the virus may become negative within 2 years, or HPV infection can persist for years in the body without causing any problems. However, women with persistent high-risk HPV infections are at the greatest risk for developing cervical cancer. A recent study showed that a sexually transmitted bacterial infection (known as trichomoniasis) has been linked to increased risk for advanced prostate cancer – the illness that strikes nearly 200,000 American men each year.

We can go on and on …

This doesn’t mean that you’ll develop cancer if you have any infection or inflammation, because infection alone usually does not lead to cancer. However, it does mean that you need to control your infection, get it treated timely, and thereafter be vigilant about any cancer risk factors and live a healthy lifestyle.

Photo credit: by Leonardini