Diarrheal Diseases: GBD 2017

Disease Description

We follow GBD 2017 and “defined diarrhoeal disease episodes as three or more loose stools in a 24-hour period.” (p. 88 of [GBD-2017-YLD-Capstone-Appendix-1]).

Diarrhea has various etiologies, with infectious diarrhea accounting for the vast majority of global diarrheal disease burden. The top pathogens responsible for diarrhea include norovirus, rotavirus, E. Coli, Camplyobacter, and Salmonella. Bacterial infections, and specifically species of Shigella, account for the majority of bloody diarrhea.

Infection most commonly occurs via feces-contamined water, and can also spread via contamined food and person-to-person contact. ([WHO])

The global prevalence of diarrhea thus varies considerably accoring to resource access. In particular, resource-limited countries have a “baseline frequency… superimposed with epidemic cases of diarrhea” ([UpToDate_1]). The top risk factors for diarrheal diseases thus include crowding (such as living in refugee camps) and poor sanitation, in addition to immune system-compromising conditions, such as living with HIV.

The most significant outcomes of a nonfatal diarrhea episode are dehydration and the loss of nutrition. In particular, in low-income countries, the high prevalence of diarrhea is a major cause of child malnutrition ([WHO]), which in turn makes such children more susceptible to future diarrheal episodes and other negative sequelae.

The WHO-recommended measures for diarrhea prevention include:

  • Access to safe drinking water;

  • Use of improved sanitation;

  • Hand washing with soap;

  • Exclusive breastfeeding for the first six months of life;

  • Good personal and food hygiene;

  • Health education about how infections spread; and

  • Rotavirus vaccination.

Noninfectious diarrhea etiologies are far less common, but are more likely among chronic cases of diarrhea. Causes of noninfectious diarrhea include ischemic colitis, inflammatory bowl disease, among others ([UpToDate_2]).

[CDC], [Wikipedia]

Modeling Diarrheal Diseases in GBD 2017

The GBD diarrheal diseases model follows a standard GBD framework, including a cause of death (CoD) model and a nonfatal model.

The CoD model estimates the cause-specific mortality rate (CSMR) within the total population, and a cause fraction. These estimates are based on vital registration and verabal autopsy data.

The nonfatal model is run in DisMod. The primary inputs are prevalence epi data, for which self-reported prevalence is the reference definition, and the CSMR estimates from CodCorrect. Separately, the ratio of mild/moderate/severe diarrhea is estimated, based on data from a systematic review. These severity ratio estimates do not vary by age/sex/location/year, and are applied to the prevalence and incidence estimates produced by DisMod to produce the three sequela of diarrheal diseases: mild diarrheal diseases, moderate diarrheal diseases, and severe diarrheal diseases. In our model, every individual will have the average severity for their age/sex/location/year.

The GBD 2017 adjusted for seasonal variation in diarrheal disease, but we have not attempted to include this variation in Vivarium yet. (p. 89)

There is substantial additional effort in GBD to divide diarrhea burden into the aetiologies of diarrhea, but we have not included aetiologies in this simple model.

GBD Hierarchy

../../../../_images/DD_cause_hierarchy.svg

Cause Model Diagram

../../../../_images/DD_cause_model.svg

S: Susceptible to diarrheal diseases

I: Infected and currently experiencing a diarrheal disease bout

Data Description

State Definitions

State

State name

Definition

S

Susceptible

Simulant currently has diarrheal disease

I

Infected

Simulant does not currently have diarrheal disease
State Data

State

Measure

Value

Notes

I

prevalence

prevalence_c302

I

birth prevalence

0

I

excess mortality rate

\(\frac{\text{deaths\_c302}}{\text{population} \,\times\, \text{prevalence\_c302}}\)

I

disability weight

\(\displaystyle{\sum_{s\in \text{sequelae\_c302}}} \scriptstyle{\text{disability\_weight}_s \,\times\, \text{prevalence}_s}\)

S

prevalence

1-prevalence_c302

S

birth prevalence

1

S

emr

0

S

disability weight

0

All

cause-specific mortality rate

\(\frac{\text{deaths\_c302}}{\text{population}}\)
Transition Data

Transition

Source State

Sink State

Value

Notes

i

S

I

\(\frac{\text{incidence\_rate\_c302}}{1-\text{prevalence\_c302}}\)

We transform incidence to be a rate within the susceptible population.

r

I

S

remission_rate_m1181

Already a rate within with-condition population
Data Sources and Definitions

Value

Source

Description

Notes

prevalence_c302

como

Prevalence of diarrheal diseases

deaths_c302

codcorrect

Deaths from diarrheal diseases

incidence_rate_c302

como

Incidence of diarrheal disease within the entire population

remission_rate_m1181

dismod

Remission of diarrheal disease within the infected population

population

demography

Mid-year population for given age/sex/year/location

sequelae_c302

gbd_mapping

List of 4 sequelae for diarrheal diseases

Note Guillain-Barre due to diarrheal diseases is included in sequelae.

prevalence_s{sid}

como

Prevalence of sequela with id sid

disability_weight_s{sid}

YLD appendix

Disability weight of sequela with id sid
Restrictions

Restriction type

Value

Notes

Male only

False

Female only

False

YLL only

False

YLD only

False

YLL age group start

Early neonatal

age_group_id = 2; [0-7 days)

YLL age group end

95 plus

age_group_id = 235; 95 years +

YLD age group start

Early neonatal

age_group_id = 2; [0-7 days)

YLD age group end

95 plus

age_group_id = 235; 95 years +

Validation Criteria

Todo

Describe tests for model validation.

References

[WHO] (1,2)

Diarrheal disease Fact Sheet. World Health Organization, 2 May 2019. Retrieved 14 Nov 2019. https://www.who.int/news-room/fact-sheets/detail/diarrhoeal-disease

[UpToDate_1]

Approach to the adult with acute diarrhea in resource-limited countries Retrieved 26 Dec 2019. https://www.uptodate.com/contents/approach-to-the-adult-with-acute-diarrhea-in-resource-limited-countries

[UpToDate_2]

Approach to the adult with acute diarrhea in resource-rich countries Retrieved 26 Dec 2019. https://www.uptodate.com/contents/approach-to-the-adult-with-acute-diarrhea-in-resource-rich-settings

[CDC]

Diarrhea: Common Illness, Global Killer. https://www.cdc.gov/healthywater/global/diarrhea-burden.html

[Wikipedia]

Diarrhea. From Wikipedia, the Free Encyclopedia. Retrieved 14 Nov 2019. https://en.wikipedia.org/wiki/Diarrhea

[GBD-2017-YLD-Capstone-Appendix-1]

Supplement to: GBD 2017 Disease and Injury Incidence and Prevalence Collaborators. Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, Disease Study 2017. Lancet 2018; 392: 178 (pp. 88-94)

(Direct links to the YLD Appendix hosted on Lancet.com and ScienceDirect)