Table 1 Operational definitions of study variables

1

Ecological regions:

1.1

Delta and lowland (heavy rainfall more than 2500 mm)

Ayeyarwady, Yangon, and Bago regions; Mon and Kayin states

1.2

Hills (moderate to heavy rainfall)

Kachin, Kayah, Chin, and Shan states

1.3

Coastal (heavy rainfall more than 2500 mm)

Rakhine state and Taninthayi regions

1.4

Plains (uneven topography and rainfall less than 1000 mm)

Magway, Mandalay, Sagaing, and Nay Pyi Taw regions

2

Disease severity grade: (WHO grading of severity of DHF)

2.1

DF

Fever with two of the following: headache, retro-orbital pain, myalgia, bone pain, rash, and hemorrhagic manifestations (No evidence of plasma leakage)

2.2

DHF grade I

Fever and hemorrhagic manifestation (positive tourniquet test) and evidence of plasma leakage

2.3

DHF grade II

As in grade I plus spontaneous bleeding

2.4

DHF grade III

As in grade I or II plus circulatory failure (weak pulse, narrow pulse pressure (≤ 20 mmHg), hypotension, restlessness)

2.5

DHF grade IV

As in grade III plus profound shock with undetectable blood pressure and pulse