Countries that have successfully achieved and maintained malaria elimination generally have an effective surveillance and appropriate response system in place to prevent disease re-introduction . Many countries in which malaria has re-emerged after coming close to elimination have failed to maintain vigilant and robust surveillance [14, 24]. As control programmes reduce the incidence of malaria, the pattern of disease also changes, necessitating extensive disease monitoring to determine the most efficient and cost-effective pre-elimination strategies . The importance of maintaining surveillance is clear with examples of large malaria resurgence in Sri Lanka in 1968  and in Madagascar between 1985 and 1990 after transmission had been interrupted  due to reduced surveillance and other control measures.
Adequate surveillance with appropriate response is essential for control and is of equal or more importance when countries or regions move towards elimination. One of the preconditions for the certification of malaria elimination by the WHO is the presence of a high quality surveillance-response system .
When countries or regions move towards elimination, monitoring and evaluation resources should trend away from the measurement of morbidity and mortality, which becomes increasingly difficult and insensitive, towards active case detection approaches as part of surveillance, followed by swift public health action to prevent foci of infections becoming epidemics [28, 29]. The Malaria Elimination Group (MEG) goes further to define the key components that comprise an effective surveillance-response system [14, 30].
It would be essential to engage the strong existing community structures in the design of a surveillance-response system in Isabel Province. Community participation in surveillance programmes in other countries has been shown to be of great benefit and contributes to the long-term sustainability of such a programme [31–33]. It has also been shown to be beneficial in other island nations and in particular in neighbouring Vanuatu where continuing community-based surveillance has helped to maintain elimination status on Aneityum island [31, 33].
High levels of disease awareness in the community along with systems of timely case reporting allow the effective implementation of a participatory surveillance-response system which is more financially and logistically feasible than widespread screening systems requiring large amounts of manpower and resources [34, 35]. This approach is important through the phases of elimination, from intensified control to 'holding the line' .
Whilst beneficial components for an effective surveillance-response system already exist in Isabel Province, the size of the task to implement an RDT based surveillance-response system must not be underestimated. With a population of around 26,000 people who travel extensively on a variety of modes of transport the preparation, planning, resources, time, human resources and funds required to set up the programme would be considerable. If implemented, it should be incorporated as an integral part of the SI National Malaria Control Programme to achieve sustainability and contribute to the strengthening of the national health system.
Since the study was performed, the Ministry of Health and the NVBDCP, SI have determined that screening all travellers entering Isabel Province at ports and airports is not currently viable due to prevailing financial and logistical constraints. Therefore it has been determined that a more informal system of surveillance by engaging community members to identify new arrivals, including returning Isabel residents, and direct them to malaria testing at the nearest health facility is more feasible . It is noted that such a system of "community eyes and ears" has existed informally to some extent for years, but now a major awareness campaign throughout the province has been recommended by health authorities to more thoroughly educate residents about this system . The responses given by our participants suggest acceptability and support for such a system. For this to be effective however RDT coverage will need to be scaled up and should be prioritized at health facilities.
When it becomes feasible for resources to be shifted towards a more formal surveillance process , a system based on RDT testing of new arrivals would be a necessary step towards more rigid surveillance. Solomon Islands can learn and be inspired by established malaria screening systems such as in international airport arrivals in Oman , Mauritius  and Zanzibar  and in some domestic airports in Vanuatu .
The implementation of such a system would require key logistical considerations such as attention to the high volume of passenger travel at holiday times and the busy and sometimes chaotic boarding and disembarking processes at the wharfs. Although less common, unscheduled inter-provincial travel by OBM poses numerous challenges for malaria surveillance. The risk that this type of travel poses on the population in Isabel Province is difficult to measure. The southern region of frequent inter-provincial OBM travel appears to overlap with areas previously identified as "hot spots" by the NVBDCP; however these areas were not corroborated by the most recent mass blood survey conducted in on Isabel Province in 2009 . Suggestions towards surveillance raised by community members such as ideas regarding the timing of testing to minimize interruption to ticketing and boarding processes should be considered. Positive cases should be treated as soon as possible and followed up by the malaria team which was also suggested by many participants. It is advantageous to provide free treatment for all these cases .
Logging activity has been previously implicated in causing increased malaria prevalence due to the change in vector ecology and to population mobility . Ideally logging camp managers should incorporate a system to ensure that all workers arriving on site from outside Isabel Province have had RDT done at some point in their journey. This implementation would require assistance from the provincial government for policy development and/or financial support.
The finding that travel to other provinces by OBM mostly occurs from two small coastal regions is an advantage for the implementation of a surveillance-response system however this type of travel still poses a significant challenge. An education and awareness campaign is an essential component to encourage compliance, to minimize confusion and to reduce stigma towards positive cases. Malaria elimination feasibility assessments in other countries have recommended that education and community involvement are essential in an elimination programme .
This study was conducted in five different villages in a relatively limited area of Isabel Province (due to logistical difficulties accessing villages further away) and was potentially not representative of the entire island. In addition, it is acknowledged that the capture of the full range of community views may have been reduced by selection of participants having been facilitated by village chiefs. However, as there was participation of key informants from across Isabel Province (as a result of the concurrent Isabel Provincial Assembly and Provincial Malaria team meetings in Buala), authors are confident that a sufficient range of perceptions and attitudes across the island were captured.
A key assumption in this study was that RDT-based surveillance programmes are an effective strategy to detect the imported reservoir of infection in this setting. The authors recognise that people with chronic low-grade infections, which may typically be characterised by gametocyte carriage, may not be detected by RDTs and yet represent an important reservoir for future malaria introduction and transmission in locations where transmission has been interrupted. In this situation, polymerase chain reaction (PCR) assays would theoretically be of value but clearly this would not be a viable option for active surveillance in rural settings in the South West Pacific. These issues require further scrutiny but were beyond the scope of this current research.
All FGDs were conducted in SI Pigin and the non-SI Pigin speaking facilitators conducted KIIs in English. Most key informants spoke English well but some may have had difficulty expressing views and opinions to their full extent due to their incomplete grasp of the language. This problem was overcome by recording sections of dialogue in Pigin and later translating it to English by the SI Pigin speaking facilitator.
Finally, data collected from Solomon Airlines and from the IDC provided some quantitative information regarding the number of passengers on flights and ships between Honiara and Isabel Province. The quality of data from the IDC was poor for some months, which resulted in limited understanding of the number of passengers travelling by ship. Unscheduled travel between provinces by OBM and by logging barges can occur almost anywhere on the island at any time and therefore quantitative data on this aspect is not recorded and impossible to obtain.
In summary, a surveillance-response system to prevent introduction and re-introduction of malaria to Isabel Province would be feasible and acceptable to the community. The study found many factors that would contribute positively towards the feasibility of such a system. The challenges are less conceptual but are within the operational planning of the National Malaria Control Programme. This study is one of few that explore the feasibility and acceptability of a surveillance-response system along with human mobility patterns. It highlights how factors influencing migration often affect poor people in malaria endemic regions and that a greater understanding of population movement can improve malaria control activities .
Success in reducing malaria transmission to such low levels in Isabel Province has been attributed to broad community participation along with the early detection and effective treatment of malaria cases. These strengths form solid foundations for the proposed surveillance-response system, which in turn will be vital to achieving and maintaining malaria elimination in Isabel Province.