Health and Community 14: Non-Communicable Disease Epidemiology

Non-Communicable Disease Epidemiology

Non-communicable disease (NCD) epidemiology focuses on making associations between risk factors and disease.
It's simpler than infectious disease epidemiology because it doesn't involve transmission between individuals.
Focuses on the interaction between the host and risk factors.

Origin of Association Studies: Sir Richard Doll

Sir Richard Doll investigated the increase in lung cancer cases in the late 1940s.
He designed a questionnaire for 650 male patients in London hospitals.
It was a retrospective study.
Patients with suspected lung, liver, and bowel cancers were surveyed; interviewers were blinded to diagnoses.
Preliminary study: small scale.

Initial Findings

Confirmed the increase in lung cancer cases was real.
Initial assumptions pointed to environmental factors like industrial pollution (smuts from coal fires, road tiring, exhaust fumes).
Doll found a strong association between smoking and lung cancer, which was unexpected.
Smoking was widely considered a harmless habit at the time; even doctors advertised it.
In the 1950s, 80% of men were smokers.
Public recognized that it did make people cough.

Publication Challenges and Follow-Up

The Medical Research Council (MRC) was allegedly hesitant to publish Doll's findings.
The MRC preferred to focus on environmental factors.
A larger follow-up study confirmed the association between smoking and lung cancer.
A study from the United States published similar findings around the same time.
Doll's work is now considered the origin story of non-communicable disease association studies due to his rigorous approach.

Doll's Approach

Obtaining good quality data to avoid biases.
Randomization to get appropriate survey responses.
Finding associations through statistical methods.
Statistically testing the associations.
Trying to disprove the association by considering other potential causes.

Retrospective Studies

Retrospective studies look backward to determine exposures and risk factors in patients with an established outcome (e.g., lung cancer).
Criticism: potential for error and bias because researchers know the outcome.
Drawback: might not ask the right questions or collect the relevant data.
In Doll's study, if they hadn't asked about smoking, they wouldn't have found the association.

Prospective Studies

Doll and Bradford Hill launched a long-term prospective study on smoking using a cohort of British doctors.
Prospective studies look forward to examine outcomes in a population, tracking risk and protective factors over time.
Fewer sources of bias compared to retrospective studies.
Drawback: takes a long time (years or decades).
The prospective study ran from 1950 to 2004 (Doll's entire career).

Results of the Prospective Study

Data showed survival rates over time based on smoking habits.
Quitting smoking at any age leads to greater survival rates.
Quitting between 25 and 34 results in similar survival rates to non-smokers.
Quitting between 35 and 44 leads to survival rates almost equal to those who never smoked.
Quitting even between 55 and 64 increases survival rates.
Confirmed the connection between smoking and lung cancer and quantified the impact.
Also identified associations with chronic bronchitis and coronary disease.
Initially, smoking was associated, but later proven to cause lung cancer.

Policy Implications and Delays

Britain started taxing tobacco a quarter of a century later.
Doll campaigned for action to reduce smoking but was disappointed by the UK government's slow response.
A ban on advertising also took decades to implement.
The UK smoking ban in 2007 prohibited smoking in indoor public places.

Spatial Distribution and Risk Factors

There is a North-South divide in lung cancer rates in the UK (data from 2012-2014).
Southwest and Southeast: ~66 cases per 100,000.
North: Over 101 to 112 cases per 100,000
This is not necessarily linked to areas of industrialization.
Four in ten cancers are thought to be avoidable.
Lifestyle and behavior significantly impact cancer rates.

Cancer Avoidability

Cancer Research UK data shows the calculated percentage avoidable for different cancers.
Prostate and testicular cancer: 0% avoidable.
Cervical cancer: 100% avoidable.
Lung cancer % avoidable due to the possibility that someone can develop it without having smoked.
Many avoidable cancers are linked to lifestyle.

Prostate Cancer: Risk Factor - Age

Incidence increases with age, peaking in the late 60s, then decreasing.
The rate of cases continues to increase until the mid-to-late 70s.
The decline is possibly due to other health issues.
Age at death increases until the early 80s.
Rate of death increases throughout.

Prostate Specific Antigen (PSA) Diagnostic Test

PSA is a protein produced by both normal and cancerous prostate cells.
Increased levels may indicate cancer (threshold: 3 nanograms/milliliter).
Advantages: can detect possible cancer before symptoms.
Early detection means potential intervention.
High PSA levels may signal a high risk of developing prostate cancer.
Disadvantages:
- A raised PSA level doesn't necessarily mean prostate cancer.
- A low PSA level doesn't mean no prostate cancer.
  - 1 in 7 with a normal PSA level may have prostate cancer.
  - 1 in 50 of those with a normal PSA level may have a fast-growing prostate cancer.
- High PSA levels might mean more tests (biopsy), with potential side effects (pain, infection, blood in urine/semen).
- Detecting slow-growing prostate cancer may be a negative if it wouldn't cause ill health anyway.
- Treatments can affect daily life with urinary, bowel, and erectile problems.
The UK has no current PSA screening.

Effect of Low-Intensity PSA-Based Screening

Study from the Journal of the American Medical Association.
Individuals aged 50-69 were screened for PSA during GP visits for any reason (intervention group; $n = 189,000$ ).
The comparison group was tested for prostate cancer only when symptoms were reported ( $n = 219,000$ ).
Low intensity refers to a single PSA test.

Results

The early study showed a large jump in the number of new cases in the intervention group.
After 14 years, a similar number of cases were diagnosed in both groups.
Cases were detected earlier in the intervention group.
Mortality rates were not significantly different between the groups.
There was a cost to initial screening.

Conclusion

Detecting cases earlier did not change mortality rates.
The screening can lead some people who were screened to falsely believe it's too late to get screened again.
Some patients became worried if they are either a true or false positive.
High-profile endorsements (Sir Chris Hoy) can influence public opinion but may not align with public health data.

Testicular Cancer: Risk Factor - Age

Peak incidence in the early 30s, declines with age.
Mortality pattern differs: early peak in late 20s to early 30s, dip, later rise in late 40s and early 50s.
Older individuals are less likely to notice symptoms or be diagnosed early.

Other Risk Factors

Having testes.
Potential association with pubertal hormones (not proven).
Differences in association with ethnicity (white males have slightly higher rates).
Cryptorchidism (undescended testicles) leads to higher rates.
Relapse (getting cancer again) is likely if an individual has had cancer before.
Association with inguinal hernia (questionable mechanism).
Variability in association with HIV diagnosis (35-79% higher risk).
Family history indicates genetic association:
- Father with testicular cancer: 4-5 times more likely.
- Brother with testicular cancer: 8-9 times more likely.
Association with height (11-13% increase in risk per 5 cm).

Survival Factors

Excess weight lowers survival by 8%.
Later puberty lowers survival by 16-19%.

Summary for prostate and testicular cancers

For both prostate and testicular cancers age is the main risk factor.
But for prostate cancer, it is increasing age that drives the risk rate.
For testicular cancer, it's a younger period of time.
The mortality pattern is different for testicular cancer compared to its incidence rate.

Cervical Cancer: 100% Avoidable

Only association: sexual activity and transmission of human papillomavirus (HPV).
HPV infection is a consequence of infection with HPV.
It is the only cancer caused by an infectious agent in humans.

Prevention and Vaccination

The UK vaccinates against HPV (girls aged 12-13 in year 8, boys as well since 2019-2020).
Originally a two-dose strategy, potentially changed to one dose.
The vaccines target the most common HPV strains.
Vaccination raises herd immunity and protects against diseases caused by HPV in both sexes (tumors of the lips, anus, penis, genital warts).
Australia, with early and comprehensive vaccination programs, predicts the elimination of cervical cancer.