Eradication effort has to permanently eliminate a pathogen everywhere in the world thereby removing the risk of reintroduction and re-establishment. Elimination, on the other hand, focuses on reduction to zero incidence of a certain pathogen in a given area, with active measures to prevent pathogen re-establishment from other areas after elimination. During an elimination process, once an infection is driven to very low levels, the ecology of pathogens may change requiring different surveillance and control strategies . Susceptible build-up, waning of immunity, increase in the age of infection, non-compliance of individuals with control measures, pathogen change and emergence of resistance as a result of intensified efforts all become increasingly important during the final stages of such programmes . Therefore, in order to achieve targets for elimination of vaccine preventable highly contagious illnesses such as measles, in addition to the maintenance of vaccination integrity, all other likely contributory factors for the illness in the community needs to be timely identified and intervened.
CNTH is the only tertiary care institution in the Gampaha district of the Western Province of Sri Lanka. Although it does not represent the status of hospitals in the whole of Sri Lanka, Western Province or the Gampaha district, the two hospitals included here are likely to represent the basic infrastructure facilities that are available in most of the government hospitals and the private sector hospitals. Firstly, the adult patients who presented to both hospitals had at least 3–4 days of admission until the diagnosis was made. The patients who were admitted to CNTH were kept in a busy medical unit, among most other patients with either acute or chronic ill health. The reasons for the delay in the diagnosis included non-awareness of its occurrence, unfamiliarity of clinical illness among adults and non-specific nature of the clinical illness that mimicked any other common acute tropical febrile illness.
Since all these patients were above 25 years of age it is likely that they had no or partial immunization against measles by natural mechanisms or through National Immunization programme. During the acute phase of illness (first 4 days) all these patients presented with an illness that mimicked acute dengue or any other common acute febrile illnesses in the tropical setting. Although they were negative by NS1 antigen they were kept under close monitoring as almost all of them had reducing or low platelet counts and derangement in hepatic enzymes. Although the development of the facial rash together with red tearing eyes suggested the possibility of measles, its diagnosis was delayed at least in the first few patients due to unfamiliarity of the illness in adults. It mimicked chikungunya fever in some cases due to severe arthralgia and the non-specific nature of the rash and its pattern of involvement . Furthermore, a similar clinical illness seems to occur in Zika virus infection  although it is yet to be documented in Sri Lanka.
Almost all of these patients were managed in a busy clinical setting and amongst other patients with acute or chronic illnesses such as diabetes mellitus, chronic liver disease or chronic kidney disease where immune deficiency is known to occur. In multi-specialty tertiary care centers there is a possibility of transmission to immune-compromised and pregnant patients as well as to non-immune staff who may in turn care for high-risk patients . Although we were not made aware of any occurrence of measles among patients or the ward staff who had close contact during the management of these patients, influx of patients with measles to busy multidisciplinary tertiary care centers during community outbreaks of measles have resulted in nosocomial outbreaks [16, 17].
Early diagnosis of measles and isolation of such patients would be the most ideal strategy in order to prevent spread and occurrence of spread to other non-immune patients or health care workers. However currently there are no early diagnostic facilities available for measles and there are no isolation facilities available in CNTH or most other major hospitals in Sri Lanka. Furthermore, it is very unlikely that such facilities would be realistic in most hospitalsof developing countries such as Sri Lanka. It is well known that acute febrile illnesses that occur in the tropics such as measles, dengue fever, typhoid fever, leptospirosis, and severe acute respiratory syndrome (SARS) can be confused with each other . At presentation, these febrile illnesses share similar clinical features, including headache, myalgia, and rash. In the case of dengue fever clinical features of dengue haemorrhagic fever, such as bleeding and plasma leakage, are seen after the initial febrile phase is subsiding, typically after the third or fourth day of fever. Similarly rash of measles although non-specific, appears after the 4th day of the illness. Therefore illnesses with similar characteristics, such as dengue, leptospirosis, measles, etc. have been found difficult to discriminate on the basis of any clinical algorithm alone . Therefore, the most important strategy to diagnose measles at a very early stage would be to develop molecular/antigen based rapid diagnostics with high sensitivity and specificity. However, it is very unlikely that such diagnostics would be developed and made available, cost effective or realistic for illnesses such as measles due to its low incidence and low mortality figures.
Although the most likely reason for measles infections in these adult patients would be the on-going low level measles infection in the community, we feel that it is important to consider other likely source of the measles virus especially in the adults. Such sources could be related to acquisition of the virus through foreign travel although none of these patients or their close contacts had a history of foreign travel closer to their being ill. This is because such infection is likely to introduce non-native genotypes of the virus resulting in severe outbreaks . Furthermore potential for introduction of new virus-genotypes should be kept in mind asworld travel is rapidly expanding for many purposes such as for education, employment and tourism. Travel has been shown to cause importation of infections such as SARS, chikungunya, dengue and Zika virus to many parts of the world resulting in outbreaks or establishment of these infections in various geographical regions [20, 21]. Therefore, there is always a risk of transmission of illnesses like measles between countries.
The combination of molecular epidemiology and standard case classification and reporting seems to be very sensitive means to describe the transmission pathways of measles. Virologic surveillance in order to monitor the viral genotypes in a particular country or region over time seems very important in order to interrupt the transmission of endemic measles . In order to address these issues, the Epidemiology Unit of Sri Lanka has implemented due measures to obtain comprehensive data collection from patients with measles including obtaining blood samples for genetic isolations . However, it was noted that such operations have either been unaware of or slowed down due to sporadic nature of measles among the adult patients (unpublished data). Therefore, intensified public awareness, periodic reminding of medical institutions and implementation of proper monitoring systems may be warranted in order to achieve current goals towards elimination of measles by the year 2020.