*2.1.3. Dose-response assessment*

The QMRA-MC was used to estimate risks of *Ascaris* and norovirus and *Salmonella* infections. The study by Navarro et al. [13] found that *Ascaris* infection data best fitted the β-Poisson dose-response equation [13]:

$$P\_l(d) = 1 - \left[1 + (d/N\_{\mathfrak{g}0}) (2^{1/a} - 1)\right]^{-a} \tag{1}$$

where *PI* (*d*) is the probability of infection in an individual (infection/event), *d* is the ingested number of *Ascaris* eggs on one occasion (eggs/event), *N*50 is the mean infective dose number of *Ascaris* eggs (eggs), *I* means considerable spice for calculation of probability (−) and *α* is an infectivity constant of *Ascaris* (−). They found the values of *N*50 and *α* to be 859 and 0.104, respectively. Since they were working with epidemiological data on *Ascaris* prevalence rather than conducting human *Ascaris* dose-challenge studies, the value found for *N*50 is not a measure of the actual median *Ascaris* infective dose, but rather an empirical value arising from their statistical analyses [14].

The annual probability of infection, *PI*(*A*) (*d*) (pppy), is given by:

$$P\_{\mathbb{N}(d)}(d) = \mathbf{1} - \left[\mathbf{1} - P\_{\!\!/\!}(d)\right]^{\mu} \tag{2}$$

Where *n* is number of events per year to the single *Ascaris* dose (−) [14]. For norovirus, the dose response data set of Teunis et al. [1] was used in place of the β-Poisson equation [14]. The β-Poisson equation was used to assess the dose response of salmonellosis. The *N*50 and *α* used are 17,700 and 0.23475 respectively.

#### *2.1.4. Exposure assessment*

• To consider the worst case, 50,000 eggs/g in wet faeces is excreted from a heavily infested person [7]. The value of the initial concentration of *Ascaris* eggs was 336 eggs/g-dry compost. This number was estimated by multiplying the number of eggs excreted per gram (50,000 eggs/g) by the 100 g of compost dividing by the bulk density of the compost.

• Highly infested person of viral infection excretes a maximum of 1011 viral copies/g in faeces from highly infected person [1, 8, 9] was used for the risk assessment taking account of the highest risk. Assuming this concentration, the initial concentration was estimated

number of norovirus excreted per gram (1011 viral copies/g) by the 100 g of the compost and

concentration, the initial concentration was estimated at 6.72 × 10<sup>7</sup> CFU/g-dry compost. This number was estimated by multiplying the number of *Salmonella* excreted per gram (1010 CFU/g) by the 100 g of the compost and dividing by bulk density of the compost.

• Ingestion rate of compost is 150–800 mg/event. This is used in the risk assessment of dioxin

• The concentration of pathogens in the compost after the post treatment was estimated using the first-order kinetic model from the earlier studies on *Ascaris* eggs and indicator MS2 bacteriophage inactivation and *E. coli*. The data from these experiments were used to

Farmers performing post-treatment would be exposed to pathogens in the compost. There are several groups of pathogens, but the pathogens of considerable interest in the study area are *Ascaris* eggs, viral infections (norovirus) and *Salmonella* because *Ascaris* and norovirus are also known to be the most resistant to treatment processes [11, 12]. Burkina Faso recorded 32.8% of bacteraemia among febrile children admitted to hospital (non-typhoid *Salmonella*) between 2012 and 2013 [2] and it is also reported that the carrier state of *Salmonella* typhi is defined as persistent shedding in faeces for greater than 12 months [2]. Accidental ingestion of a small dose consequently implies a high risk of infection compared to many other pathogens [10].

The QMRA-MC was used to estimate risks of *Ascaris* and norovirus and *Salmonella* infections. The study by Navarro et al. [13] found that *Ascaris* infection data best fitted the β-Poisson

(*d*) = 1 − [1 + (*d*/*N*50)(21/*<sup>α</sup>* − 1)

]

<sup>−</sup>*<sup>α</sup>* (1)

viral copies/g-dry compost. This number was estimated by multiplying the

–1010 per gram of faeces [3]. Assuming this

at 6.72 × 10<sup>8</sup>

110 Agricultural Waste and Residues

in soil ingestion rate [10].

*2.1.2. Hazard identification*

*2.1.3. Dose-response assessment*

dose-response equation [13]:

*PI*

dividing by bulk density of the compost.

• Concentration of *Salmonella* spp. in faeces is 104

• Post-treatment would be done every 4 months.

re-estimate the inactivation rate co-efficient [6]. • The moisture content of all treatments was 50%. The human exposure assumed to take place is an event when farmers work on compost. Practically, one egg is enough to cause an infection. Norovirus has an extremely low infectious dose [9] and salmonellosis is a public health concern in Burkina Faso [2].

#### *2.1.5. Risk characterisation*

The Monte Carlo technique has been used to evaluate the infection risk. The random number is applied for estimation of variables with distributions for simulation of Eqs. (1) and (2). The simulation was repeated 10,000 times [14]. Then, 95 percentile of the probability was estimated as the infection risk.
