2.7 Estimation of treatment resource needs

2.7.1 Number of patients expected

Estimate the number of cases that can be expected in the outbreak to determine the resources needed for case management.

The calculation requires applying a representative attack rate (AR) to the total population of the at-risk community. An appropriate AR can be obtained from previous outbreaks in the area.
If historical data are not available or are deemed to be incomplete or unreliable, an AR typical for the given context can be chosen (Section 1.1.7).
Keep in mind that an AR derived from historical data or selected as typical for the specific context is only an approximation.
An outbreak can be expected to be severe if it occurs earlier in the season than usual or if a large number of people or locations are affected during the first weeks.

For an example of calculation of the number of expected cases, see Box 2.1.

2.7.2 Peak bed capacity

Sufficient bed capacity is essential, particularly at the peak of the epidemic. Estimating peak bed capacity while still in the early phase of an outbreak gives planners and logistic services an idea of the size and number of cholera facilities that will be required.

The calculation of peak bed capacity is based on the total number of patients expected and the following assumptions derived from previous experience:

– 25-30% of patients will have severe dehydration, 30-40% some dehydration, and 30-40% no dehydration.

– All patients with severe dehydration and approximately half of patients with some dehydration will need a bed for at least a night.

Based on these two first assumptions, approximately 50% of all cholera patients seeking medical care will need a bed.

– The combined average length of stay for patients hospitalized with some and severe dehydration is 2 days (length of stay can be shorter in settings with easy access to care and longer in settings with difficult access or more complicated patients such as the elderly or pregnant women).

– Approximately 15-20% of patients will seek medical care during the peak week (less for rural settings, more for crowded urban settings).

These estimated values can be adjusted to fit the local context if sufficiently reliable detailed data from prior outbreaks are available.

For an example of calculation of peak bed capacity required, see Box 2.1.

Box 2.1 - Number of expected cases and peak bed capacity required

Examples of calculations according to the context

Refugee camp
Population of 30 000. Attack rate: 5%. Proportion of caseload admitted during 1 week at the peak of the outbreak: 20%. Average length of stay: 2 days. Proportion of cases needing a bed: 50%.
30 000 x 0.05 = 1500 cases in total
1500 x 0.20 = 300 cases during 1 week at peak
300 x 0.50 = 150 cases requiring a bed during 1 week, or 21 cases per day (150/7)
21 x 2 days = 42 total bed capacity at peak
==> 1 CTC with 50 beds

Urban area
Population of 600 000. Attack rate: 2%. Proportion of caseload admitted during 1 week at the peak of the outbreak: 15%. Average length of stay: 2 days. Proportion of cases needing a bed: 50%.
600 000 x 0.02 = 12,000 cases in total
12 000 x 0.15% = 1800 cases during 1 week at peak
1800 x 0.50 = 900 cases requiring a bed during 1 week, or 128 cases per day (900/7)
128 x 2 days = 257 total beds at peak
==> 250 beds distributed among 2 CTCs

Rural area
Population of 200 000. Attack rate: 1%. Proportion of caseload admitted during 1 week at the peak of the outbreak: 15%. Average length of stay: 2.5 days. Proportion of cases needing a bed: 50%.
200 000 x 0.01 = 2000 cases in total
2000 x 0.15% = 300 cases during 1 week at peak
300 x 0.50 = 150 cases requiring a bed during 1 week, or 21 cases per day (150/7)
21 x 2.5 days = 52 total beds at peak
==> 50-60 beds distributed among 3-5 CTUs

2.7.3 Treatment supplies

Items for curative care

The initial estimation of needs is based on the number of expected cases, taking into account known available existing stock, if any.

The calculations presented in the Table 2.1 are based on the following standards: 10 litres of ORS per patient, 8-10 litres of RL per patient with severe dehydration, 1 infusion set for 2 litres of RL, 1 catheter for 3 litres of RL, an antibiotic therapy for patients with some (= moderate) and severe dehydration, zinc sulfate for all children under 5 years.

Table 2.1 - Examples of calculations for determining medication supply needs

Refugee camp

Estimated
%

Number of cases
(population 30 000)

Essential items for rehydration

Attack rate

5%

30 000 x 0.05 = 1500

No dehydration

40%

1500 x 0.40 = 600

10 l ORS x 600 cases = 6000 sachets ORS

Some dehydration

35%

1500 x 0.35 = 525

10 l ORS x 525 cases = 5250 sachets ORS

Severe dehydration

25%

1500 x 0.25 = 375

10 l ORS x 375 cases = 3750 sachets ORS
10 l RL x 375 cases = 3750 litres RL
+ 1900 infusion sets + 1300 catheters


Complementary treatments

Doxycycline

60%

1500 x 0.60 = 900

3 tab x 900 cases = 2700 tab

Zinc sulfate

20%

1500 x 0.20 = 300

10 tab x 300 cases = 3000 tab

Urban area

Estimated
%

Number of cases
(population 600 000)

Essential items for rehydration

Attack rate

2%

600 000 x 0.02 = 12 000

No dehydration

40%

12 000 x 0.40 = 4800

10 l ORS x 4800 cases = 48 000 sachets ORS

Some dehydration

35%

12 000 x 0.35 = 4200

10 l ORS x 4200 cases = 42 000 sachets ORS

Severe dehydration

25%

12 000 x 0.25 = 3000

10 l ORS x 3000 cases = 30 000 sachets ORS
10 l RL x 3000 cases = 30 000 litres RL
+ 15 000 infusion sets + 10 000 catheters


Complementary treatments

Doxycycline

60%

12 000 x 0.60 = 7200

3 tab x 7200 cases = 22 000 tab

Zinc sulfate

20%

12 000 x 0.20 = 2400

10 tab x 2400 cases = 24 000 tab

Rural area

Estimated
%

Number of cases
(population 200 000)

Essential items for rehydration

Attack rate

1%

200 000 x 0.01 = 2000

No dehydration

30%

2000 x 0.30 = 600

10 l ORS x 600 cases = 6000 sachets ORS

Some dehydration

40%

2000 x 0.40 = 800

10 l ORS x 800 cases = 8000 sachets ORS

Severe dehydration

30%

2000 x 0.30 = 600

10 l ORS x 600 cases = 6000 sachets ORS
10 l RL x 600 cases = 6000 litres RL
+ 3000 infusion sets + 2000 catheters


Complementary treatments

Doxycycline

70%

2000 x 0.70 = 1400

3 tab x 1400 cases = 4200 tab

Zinc sulfate

20%

2000 x 0.20 = 400

10 tab x 400 cases = 4000 tab

Buffer stock

A buffer stock of at least 2 weeks should be added from the start (and maintained for the duration of the epidemic). This period can be prolonged (e.g. 3 weeks) for zones that are difficult to access or in case of supply difficulties.

For example, in a refugee camp, 1500 patients are expected (21 patients per day at peak): add the treatment of 300 patients (21 cases x 14 days = 294 patients) or 20% of patients (300 = 20% of 1500). Among these 300 patients, 75% (225 patients) will be treated by oral route only and 25% (75 patients) by oral and IV route.

Total estimated quantities

Thus it is estimated that in this refugee camp the following may be needed during the epidemic (rounded quantities):


For expected cases

Buffer stock

Total

ORS sachets

15 000

3000

18 000 sachets of ORS

RL litres

3750

750

4500 litres of RL

Infusion sets

1900

375

2300 infusion sets

Catheters

1250

250

1500 catheters