Epi in the News

1. Is this an incidence or prevalence measure?

This is an incidence measure because the study looks at the increased risk of death for some time after the infection. It measures the rate of new deaths after the infection period rather than the prevalence of deaths among chikungunya patients.

2. (Not from the article) How did this virus get its name?

The name "chikungunya" originates from a word in the Kimakonde language spoken in Africa where the virus was first discovered. The word means "to become contorted" or "that which bends up." This refers to the severe joint and muscle pains that are a common symptom of chikungunya virus infection. Patients often develop a very painful hunched-over posture due to the disabling pain. The descriptive Kimakonde name for this striking symptom is what gave the virus its name when it was first identified in humans in the 1950s.
(Web-search)

3. In epidemiologic terms, what is the mosquito?

The mosquito itself would be termed a VECTOR. However, the mosquito bite would be the exposure.

4. What is the PICO? What RR figure is estimated here?

P - People infected with chikungunya virus
I - Unexposed individuals (without chikungunya infection)
C - Comparison between the infected and unexposed groups
O - Risk of death

The risk ratio (RR) figure estimated is:
In the first week, infected individuals were 8 times more likely to die than unexposed individuals. Therefore, the estimated RR = 8

5. Can you think of some underlying differences between the people I & C groups in the PICO, above? Why do these differences matter?

Access to medical care might be different between the I&C and this could affect the outcome.

Age could also be an underlying difference. Older people are more likely to have a higher risk of more severe outcomes and death from the infection compared to younger people. If the infected group contains more elderly people, it could bias the risk ratio.

Socioeconomic status- If the infected group is more likely to be disadvantaged, it could worsen their outcomes relative to higher socioeconomic status (SES) unexposed individuals.
These differences matter because they could confound or modify the causal relationship between chikungunya infection and death risk.

6. What are the mediating factors (causal pathway) between exposure and outcome? Why does knowing about these mediators matter?

Immune response could be on the causal pathway. The inflammatory response triggered by infection may become dysregulated, leading to severe issues like organ failure.
A higher viral load from infection may cause more severe disease and increase the likelihood of death.
Immunocompromised individuals have a higher chance of getting severe secondary infections such as bacterial or fungal infections.

It is important to understand these mediators because it strengthens the causal link between exposure and outcome, and can identify targets for treatments or preventative interventions.

7. (For you to speculate) The Deccan Herald's editors felt that a study conducted in Brazil would be of interest to its readers in South India. What makes this study's results generalizable (or not) to India?

To some extent, the study results from Brazil may be generalizable to India due to similarities in chikungunya virus transmission patterns, population immunity, and healthcare system capacity constraints between the two countries, but it is important to note that variations in virus mutations, population genetics, and underlying comorbidities may affect health outcomes in each setting differently.

8. Do we need to do an RCT to prove causation?

It would not be ethical to conduct an RCT for an infectious disease such as this. However, causality can still be proven through animal models and experiments. This approach would allow for the demonstration of causal biological mechanisms that link the virus to pathways that lead to death.