WHO gives indoor use of DDT a clean bill of health for controlling malaria - Vestergaard Frandsen responds
 
We would like to make 3 things very clear:
 
ONE
There is no controversy between Indoor Residual Spraying (IRS) and Bed-nets, there is a role for both and both are important and it will never be in the interest of millions of children to begin an argument of either or.
 
Having said that, the use of insecticide-treated bed-nets is the most well proven malaria prevention tool on earth. The Cochrane review1, which is the most methodologically vigorous irrefutable evidence ever produced on malaria prevention, provides the clear evidence for bed-net’s solid basis in science.
 
The persistent call for DDT is perhaps more suitable to the media than for evidence-based public health programmes. What we need now is to not loose focus on bed-nets just because they aren’t controversial and attention grabbing! Millions of children are still dying from the world’s most preventable disease, and what we need to do right now, is to get more and more children under bed-nets in Africa!
 
TWO
On the other hand, IRS, if correctly used, can also provide similar levels of community protection. There are, however, two fundamental differences between IRS and bed-nets:
 
1) Indoor Residual Spraying is dependent on coverage while bed-nets are not. One net in one house will protect a family. This is not the case for Indoor Residual Spraying. Indoor Residual Spraying requires that a minimum of 80% of all houses within a target region be sprayed before it serves as an efficacious intervention – and IRS does not protect individuals, the way bed-nets do2.
2) IRS requires repeat intervention while bed nets no longer need repeat intervention3. Nets used to be filled with problems primarily due to re-treatment because the standard nets had to be treated with insecticide every few month to maintain their level of protective efficacy. The scientific and commercial community has since responded to produce Long Lasting Insecticidal Nets to solve this major problem of re-treatment. Today we have nets that will last multiple years 4.
  Indoor Residual Spraying still faces the same operational challenges that have made the world move away from standard nets to Long Lasting Nets, namely IRS requires repeat application5 every four to six months in every house, in every room. Admittedly in the case of DDT a few month longer but still repeat intervention. In remote, rural, resource poor areas repeat application is just not operationally suitable.
 
THREE
The statement from WHO fails to mention a number of logistical, safety, acceptability and cost-effectiveness data that needs to be considered before introducing any IRS programme
1) Have we considered what countries need to have in place for reintroduction of DDT?
  For the safe use of DDT, WHO’s frequently asked questions (FAQ)6 document raises the following issues:
 
Arrow Well developed infrastructure to reach the most rural areas
Arrow Good roads to be able to transport persistent organic pollutants
Arrow Cars to transport persistent organic pollutants
Arrow Safe storage of persistent organic pollutants
  According to WHO’s FAQ on DDT – “Every effort should be made to protect human health adequately and to prevent insecticide release into the environment – this applies especially to insecticide storage and transportation” – which means, ensuring that we spray inside houses is not enough.
  Furthermore, the Stockholm Convention7 states that the goal is to reduce and ultimately eliminate the use of DDT. With this goal in mind, each country using DDT should develop and implement an action plan. The plan should include implementation of suitable alterative products, methods and strategies, including resistance management strategies, finding an alternative viable to DDT that pose less risk to human health.
  There are 11 insecticides recommended by WHOPES for IRS against malaria vectors, why would you reintroduce DDT when there are other insecticides that are safe, highly effective and affordable8?
  Additionally we need:
 
Arrow Effective regulatory mechanisms to ensure that DDT is not used for non-recommended purposes such as agriculture
Arrow Safe spraying equipment and personal protective equipment – to ensure reduced human health risk – and use it while spraying in 40c.
Arrow Well trained personnel to conduct the spraying – too often we see failure due to simple things such as spraying on the outside of houses.
Arrow A thorough Information, Education and Communication programme which reaches all in the community and which informs them of the risk of the chemical in use.
Arrow And a monitoring and evaluation component covering all the above.
2) Resistance management
  Why would you put at risk millions of children by reintroducing DDT – a world champion in creating resistance to insecticides thereby ruining the efficacy of other perfectly capable prevention tools, such as bed-nets?
  In general, you need to continuously rotate insecticides to avoid creating resistance – proper resistance management anyway rules out repeated use of DDT – if introduced at all.
3) Human health hazards 9 10
  Scientists might have different interpretations of specific studies and findings, but to pretend that there is no evidence of association between DDT and miscarriage, preterm birth, and shortened duration of lactation is simply unwarranted – even at levels known to occur from indoor spraying only.
4) Refusal rates11
  What we have seen is that indoor spraying is very popular in the beginning, but refusal rates grow among households not allowing spray teams to enter their homes and move their furniture – documented in the 60’ and 70’ in India, Sri Lanka – and in 2002 in Kwazulu-Natal with DDT leaving stains on walls, which residents then re-plaster or wash off.
5) Cost12 13 14
  So far not a single study shows that DDT is more cost effective than Long-Lasting Insecticidal-Nets
  Has there has ever been complete cost evaluation of a spray round or the cost evaluation of a population covered with DDT which includes all the commodities and all the infrastructural costs?
  But what should be undisputable is that in the remote rural areas of Africa where death rates are the highest and where the poorest people live, bed-nets are likely to be the most cost effective – and bed-nets work in rural Africa.
6) And last – Can we reach more than 80% of the homes – and can we have repeat application – if not go for bed-nets.
 
1 Lengeler C. Insecticide-treated bed nets and curtains for preventing malaria. Cochrane Database Syst Rev. 2004;(2):CD000363. Review.
2 Centers for Disease Control and Prevention, Malaria, Vector Control http://www.cdc.gov/malaria/control_prevention/vector_control.htm
3 Lengeler C., Sharp B. Indoor Residual Spraying and Insecticide-treated Nets in Reducing Malaria’s Burden.
  Evidence of Effectiveness for Decision Makers    http://globalhealth.org/assets/publications/malaria.pdf
4 WHO Pesticide Evaluation Scheme (WHOPES) http://whqlibdoc.who.int/hq/2004/WHO_CDS_WHOPES_2004.8.pdf
5 Frequently asked questions on DDT use for disease vector control http://www.who.int/malaria/docs/FAQonDDT.pdf
6 Frequently asked questions on DDT use for disease vector control http://www.who.int/malaria/docs/FAQonDDT.pdf
7 Stockholm Convention on Persistent Organic Pollutants http://www.pops.int/
8 http://www.who.int/malaria/cmc_upload/0/000/012/604/IRSInsecticides.htm
9 Rogan WJ, Chen A. Health risks and benefits of bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT).
  Lancet. 2005 Aug 27-Sep 2;366(9487):763-73. Review.
10 Rogan WJ, Chen A. Risks and benefits of DDT. Lancet. 2005 Nov 19;366(9499):1771-2; author reply 1772.
11 Mnzava AE, Sharp BL, Mthembu DJ, le Sueur D, Dlamini SS, Gumede JK, Kleinschmidt I.
  Malaria control--two years' use of insecticide-treated bednets compared with insecticide house
  spraying in KwaZulu-Natal. S Afr Med J. 2001 Nov;91(11):978-83.
12 Curtis CF, Maxwell CA, Finch RJ, Njunwa KJ.A comparison of use of a pyrethroid either for house
  spraying or for bednet treatment against malaria vectors. Trop Med Int Health.    1998 Aug;3(8):619-31.
13 Goodman CA, Coleman PG, Mills AJ. Cost-effectiveness of malaria control in
  sub-Saharan Africa. Lancet. 1999 Jul 31;354(9176):378-85.
14 Morel CM, Lauer, JA, Evans DB. Cost effectiveness analysis of strategies to combat malaria
  in developing countries. BMJ. 2005 Dec   3;331(7528):1299. Epub 2005 Nov 10.
  Erratum in: BMJ. 2006 Jan 21;332(7534):151 and BMJ. 2006 Jul 8;333(7558):86.