Public health services – Classification and Patterns of Disease (Senior 4 Biology) | Ganzaa

Classification and Patterns of Disease

Lessons

Senior 4 · Biology

Classification and Patterns of Disease

5 lessons

Lesson 5 of 5

Public health services

25 min

A fever at nine at night

In a village in Nyaruguru, a three-year-old starts shivering with fever after dark. Her mother does not walk to a hospital. She knocks on the door of a neighbour, one of the village's community health workers, who pricks the child's finger, runs a rapid malaria test, sees two lines, and gives the first dose of an antimalarial medicine with instructions for the rest. She records the case on her phone. If the child had shown a danger sign, such as convulsions or being unable to drink, the health worker would have sent her straight to the health centre, and from there to the district hospital if needed. The family's health insurance pays most of the cost.

None of this is hospital medicine. It is public health: organised, population-wide work that prevents disease, finds it early and treats it close to home. This lesson looks at how Rwanda organises it, and how to judge whether it works.

Definition

Public health: the science and practice of preventing disease, prolonging life and promoting health through the organised efforts of society, for whole populations rather than single patients.

Primary health care: essential, affordable care delivered close to where people live, such as at community and health-centre level.

Disease surveillance: the continuous collection and analysis of data on cases of disease, so that outbreaks are detected early and control measures are judged.

Herd immunity: indirect protection of susceptible people that occurs when so many others are immune that the pathogen cannot spread effectively.

Basic reproduction number, $R_{0}$ : the average number of people one infectious person infects in a population where everyone is susceptible.

Community-based health insurance (CBHI, mutuelle de santé): a scheme in which households pay a yearly contribution and members then pay only a small part of the cost of care.

What public health services do

Function	What it involves	Rwandan example
Health promotion and education	Helping people choose healthy behaviours	Campaigns on handwashing, nutrition, and the dangers of alcohol, tobacco and drugs
Disease prevention	Vaccination, nets, screening, family planning	Routine childhood vaccination; HPV vaccination of girls; blood pressure screening drives
Surveillance and outbreak response	Detecting, investigating and controlling outbreaks	Tracing contacts, isolating patients and protecting health workers during the 2024 Marburg outbreak
Environmental health	Safe water, sanitation, food safety, vector control	Indoor residual spraying against mosquitoes; improved water sources and latrines
Accessible health care	Care at the lowest level that can provide it, with referral upwards	Community health workers, health posts and health centres, district and referral hospitals
Health financing	Making care affordable for everyone	Community-based health insurance (mutuelle de santé)

How Rwanda's health system is organised

Health services are provided at several levels: in communities, at health posts, at health centres, at district hospitals and at referral hospitals (Ministry of Health). In each village of about 100 to 150 households, the community elects health workers: a male and female pair (a binôme) who test and treat children for common illnesses and treat malaria at all ages, and a maternal health worker (animatrice de santé maternelle) who follows up pregnant women and newborn babies and encourages births in health facilities.

The pyramid works because most illness is simple and common. A rapid malaria test, oral rehydration solution or a course of tablets can be given near home, quickly and cheaply, and only the cases that need more are referred upwards. This saves lives in two ways: treatment starts sooner, and hospitals are free for the patients who really need them.

Measuring success: Rwandan indicators

Indicator	Value	Source and year
Children aged 12 to 23 months with all basic vaccinations	96 % (75 % in 2005)	Rwanda DHS 2019–20
Households using an improved source of drinking water	80 % (73 % in 2014–15)	Rwanda DHS 2019–20
Rural households more than 30 minutes (round trip) from drinking water	41 %	Rwanda DHS 2019–20
Households with at least one member with health insurance	86 % (73 % of the poorest fifth, 96 % of the richest)	Rwanda DHS 2019–20
Malaria cases treated by community health workers	57 %	RBC, fiscal year 2018–19
Drug-sensitive TB patients treated successfully	90.5 %	RBC, 2022–23 cohort

Herd immunity: why vaccination protects the unvaccinated

If one infectious person infects $R_{0}$ others in a fully susceptible population, an outbreak grows. If a proportion $p$ of people are immune, each case infects on average only $R_{0} (1 - p)$ others. The outbreak dies out when this falls below 1:

R_0(1 - p) < 1 \quad \Rightarrow \quad p > 1 - \frac{1}{R_0}

The value $p_c = 1 - \frac{1}{R_0}$ is the herd immunity threshold. The more contagious a disease (the larger $R_{0}$ ), the closer to 100 % immunity must be. Babies too young to be vaccinated and people who cannot be vaccinated for medical reasons are protected only if enough others are immune.

Worked example 1: what coverage does measles need?

Published estimates of $R_{0}$ for measles are 12 to 18. (a) Calculate the herd immunity threshold for $R_{0} = 15$ . (b) If the vaccine protects 97 % of the children who receive it, what vaccination coverage is needed? (c) Compare a disease with $R_{0} = 4$ .

(a) $p_c = 1 - \frac{1}{15} = 0.933$ , so 93.3 % of the population must be immune.
(b) Only 97 % of vaccinated children become immune, so the coverage $v$ must satisfy $0.97\,v = 0.933$ : $v = \frac{0.933}{0.97} = 0.962$ About 96 % of children must be vaccinated. Rwanda's 96 % basic vaccination coverage (DHS 2019–20) is right at this edge, which is why every missed child matters.
(c) $p_c = 1 - \frac{1}{4} = 0.75$ : only 75 % need to be immune. Measles needs much higher coverage because each case infects so many more people.

Worked example 2: is health insurance reaching the poor?

In the 2019–20 DHS, 73 % of households in the poorest fifth had at least one insured member, compared with 96 % in the richest fifth. (a) Calculate the gap in percentage points and the ratio. (b) Evaluate what these figures show about the scheme.

(a) Gap: $96 - 73 = 23$ percentage points. Ratio: $\frac{96}{73} = 1.3$ : a richest-fifth household was about 1.3 times as likely to be insured.
(b) Coverage is high overall (86 %), so the scheme reaches most families, which protects them from large health bills. But the poorest households, who are most at risk of malaria and malnutrition (Lesson 2), are the least covered, so cost may still stop some of them seeking care. A fair evaluation praises the high coverage and asks how contributions and exemptions for the poorest could close the gap. "At least one member insured" also does not show whether every member is covered.

WHO Regional Office for Africa: "Rwanda – Progress towards Universal Health Coverage". Watch for the roles of community health workers, health centres and community-based health insurance.

Warning

Common mistakes

Thinking public health means hospitals. Most public health work happens before anyone is ill: vaccines, clean water, latrines, nets, health education and surveillance.
Saying vaccination protects only the person vaccinated. Above the herd immunity threshold it also protects babies and others who cannot be vaccinated.
Judging a service by one average. A high national figure can hide gaps between rich and poor, urban and rural, or between districts.
Using $1 - \frac{1}{R_0}$ as the vaccination target without allowing for vaccine efficacy below 100 %.

Tip

Memory hook. Public health in three P's: Promote (education), Prevent (vaccines, water, nets, screening), Protect (surveillance and outbreak response). And for herd immunity: "one over R-nought, taken from one".

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Practice: public health services

Name the five levels of Rwanda's health system, from the village upwards.
State two tasks of the binôme and one task of the maternal health worker in a village.
Explain why treating malaria at village level reduces deaths and also reduces transmission.
A disease has $R_{0} = 6$ . Calculate the herd immunity threshold as a percentage.
For the disease in question 4, the vaccine protects 90 % of those vaccinated. Calculate the vaccination coverage needed.
Explain how a disease surveillance system helped Rwanda end the 2024 Marburg outbreak.
In the DHS 2019–20, 41 % of rural households needed more than 30 minutes to collect drinking water. Explain how this could affect the incidence of diarrhoeal disease, and suggest one public health response.
Evaluate the statement: "Rwanda's public health system no longer needs to change, because vaccination coverage is 96 %."

Show answersHide answers

Community health workers in the village; health posts; health centres; district hospitals; referral hospitals (including national referral and teaching hospitals).
Binôme: test and treat malaria; assess and treat common childhood illnesses; screen for malnutrition and refer (any two). Maternal health worker: identify and follow up pregnant women and newborns, and encourage births in health facilities.
Treatment starts within hours, before malaria becomes severe, so fewer children die. Clearing the parasites from the patient's blood quickly means mosquitoes that bite the patient later do not pick up the parasite, so fewer new infections follow.
$1 - \frac{1}{6} = 0.833$ , so 83.3 %.
$v = \frac{0.833}{0.90} = 0.926$ , so about 93 % coverage.
Surveillance detected and confirmed the first cases, so the outbreak was declared on 27 September 2024. Contacts of each case were traced, monitored and isolated if they fell ill; cases were counted daily, so the response could see where spread was happening (mainly among health workers) and protect them. The outbreak was declared over only after 42 days with no new case, a decision that needs reliable surveillance data.
Long distances mean households collect less water and may store it for longer or use unsafe nearer sources, so less handwashing and more faecal contamination: higher incidence of diarrhoea and a risk of cholera. Responses: build protected water points closer to homes, promote household water treatment (boiling or chlorination) and latrines with handwashing stations.
Disagree. High vaccination coverage is a real success, but it is close to the herd immunity threshold for measles, so it must be kept up every year. Other indicators show gaps: two rural households in five still need more than 30 minutes to fetch drinking water, insurance is lower among the poorest, malaria rose again in 2024, and most people with hypertension or mental disorders are not diagnosed or treated. The system must keep adapting to new threats such as non-communicable diseases and drug resistance.

Quick check

Put the levels of Rwanda's health system in order, from the village upwards.

Tap the cards in the right order.

Key points

Public health is organised, population-wide work: promoting health, preventing disease (vaccines, water, nets, screening), surveillance and outbreak response, environmental health, accessible care and fair financing.
Rwanda's system runs from community health workers in every village through health posts, health centres and district hospitals to referral hospitals, with referral up and follow-up down.
Herd immunity threshold: $p_c = 1 - \frac{1}{R_0}$ ; divide by vaccine efficacy to get the coverage needed.
Judge services with indicators (vaccination 96 %, insured households 86 %, improved water 80 % in DHS 2019–20) and look for gaps between groups, not only national averages.

1A fever at nine at night

2What public health services do

3How Rwanda's health system is organised

4Measuring success: Rwandan indicators

5Herd immunity: why vaccination protects the unvaccinated

A fever at nine at night

What public health services do

How Rwanda's health system is organised

Measuring success: Rwandan indicators

Herd immunity: why vaccination protects the unvaccinated