Economic evaluation of Chagas disease screening of pregnant Latin American women and of their infants in a non endemic area

Abstract

Migration is a channel through which Chagas disease is imported, and vertical transmission is a channel through which the disease is spread in non-endemic countries. This study presents the economic evaluation of Chagas disease screening in pregnant women from Latin America and in their newborns in a non endemic area such as Spain. The economic impact of Chagas disease screening is tested through two decision models, one for the newborn and one for the mother, against the alternative hypothesis of no screening for either the newborn or the mother. Results show that the option “no test” is dominated by the option “test”. The cost effectiveness ratio in the “newborn model” was 22 €/QALYs gained in the case of screening and 125 €/QALYs gained in the case of no screening. The cost effectiveness ratio in the “mother model” was 96 €/QALYs gained in the case of screening and 1675 €/QALYs gained in the case of no screening. Probabilistic sensitivity analysis highlighted the reduction of uncertainty in the screening option. Threshold analysis assessed that even with a drop in Chagas prevalence from 3.4% to 0.9%, a drop in the probability of vertical transmission from 7.3% to 2.24% and with an increase of screening costs up to  €37.5, “test” option would still be preferred to “no test”. The current study proved Chagas screening of all Latin American women giving birth in Spain and of their infants to be the best strategy compared to the non-screening option and provides useful information for health policy makers in their decision making process.

Introduction

Chagas disease is a parasitic disease caused by Trypanosoma cruzi. The disease is endemic in Latin America and shows very heterogeneous levels of prevalence across, as well as within countries. The vector responsible for spreading the parasite is a bug living in the poor rural areas as well as in the outskirts of the main urban centres: this makes Chagas a disease of poorer people (WHO, 2002).

The acute infection, consisting in a self-limited febrile illness, is often unrecognized. The acute phase of the infection precedes the chronic phase. It is estimated that around 30–40% of chronically infected individuals will develop symptomatic heart or gastrointestinal diseases, usually between 10 and 25 years after contracting the infection. The indeterminate phase is the period of infection with neither symptoms nor signs of cardiac/gastrointestinal tract involvement. Around two thirds of the infected people remain in the indeterminate phase for life (Rassi et al., 2010).

The current treatment for Chagas disease consists in Benznidazole or Nifurtimox. The efficacy of these two drugs depends on the age of the patient, and on the time since the infection is established: best therapeutic results are shown in acute or recent infections, and cure rates close to 100% have been reported in children treated in the first year of life (Oliveira et al., 2010, Viotti et al., 2009). Beneficial effects of antiparasitic treatment in adult chronic infections remain debated (Sosa Estani et al., 1998).

Chagas disease is a public health issue in non-endemic countries as a consequence of a social phenomenon characterizing the same subset of poor people that are most exposed to Chagas disease in endemic areas: migration (Frank et al., 1997, Schmunis, 2007). Immigrants from Latin America are not the only potential victims of the disease. In non-endemic areas, transmission through blood derivates, organ transplant and through vertical transmission is an increasing problem (Munoz et al., 2007, Piron et al., 2008, Tibayrenc and Telleria, 2010). Spain is a frequent destination of immigration from Latin America. Currently, around 1.7 million migrants from endemic Latin-American countries live in Spain. The Bolivian community, the group most affected by Chagas disease, is composed of 236,048 immigrants and 103,291 of them are women of fertile age (Instituto Nacional Estadistica (INE))

The magnitude of Chagas disease in Spain has been shown in a study conducted at the maternity wards of two hospitals of Barcelona (Munoz et al., 2009). Results showed a prevalence of Chagas of 3.4% among Latin American pregnant women and a vertical transmission rate of 7.3%. Considering that 707,000 Latin American women of fertile age were present in Spain at the time of the study and assuming one pregnancy only per woman, the study highlighted the possibility to have around 1750 infected newborn over about 10 years.

Pregnancy and delivery of Latin American women living in Spain are crucial moments for the Spanish National Health System (SNHS) to detect and treat the disease: antenatal clinic attendance is one of the most certain contacts, often the only one, Latin American women experience with the SNHS (Gascon and Pinazo, 2008).

Because of the high variability of prevalence of the disease across and within endemic countries, it would be difficult to identify which women from Latin America should receive T. cruzi screening and which should not, by simply depending on their country of provenience. At the same time, many screening tests offer a cheap and precocious diagnosis of Chagas and, especially in infants, they allow to start an early treatment which could avoid almost all negative consequences of the progression of the disease later in life.

Just a few economic evaluations have been conducted on Chagas disease interventions (Basombrio et al., 1998, Castillo-Riquelme et al., 2008, Miyoshi et al., 1994, Vazquez-Prokopec et al., 2009, Wilson et al., 2005), with only one focusing on the economic aspects of congenital transmission in an endemic area (Billot et al., 2005).

This is the first study analysing the economic convenience of undertaking Chagas disease screening to all pregnant women from Latin America in a non endemic area, providing decision makers with a model able to assess which is the best option between screening or not screening. To do this, the current study aims to evaluate the convenience of undertaking Active Detection of the Infection (ADI) in all Latin American pregnant women in Spain when they attend the antenatal clinic (ANC) and if they have a positive result, then an ADI is repeated in their newborn. The intervention includes treatment to mother and children with positive screening results. Two decision models using epidemiological data with reference to the study conducted in Barcelona is estimated (Munoz et al., 2009). Economic data were collected at one of the hospitals where the vertical transmission study was undertaken. Both costs and benefits of the screening are considered. Benefits are the avoided costs, thanks to a precocious diagnosis, of treating Chagas disease sooner rather than later in life, when the disease would be much more developed.