Understanding of sentinel surveillance

Surveillance is a much talked topic in Public health course. This is an integral important part of in any health system for making it more responsive. However, we get muddled hearing number of terms that come with surveillance, especially when you are newbies to the surveillance system in health care. One of the frequently cited words among surveillance is sentinel surveillance. 

Surveillance is defined as “the ongoing, systematic collection, analysis, interpretation, and dissemination of data regarding a health-related event for use in public health action to reduce morbidity and mortality and to improve health”. Surveillance system keeps the track of any disease/conditions/risk factors and identifies any possibility of any outbreaks or epidemic early, helping to take steps for preparedness including early detection and treatment or management.

Surveillance can be categorised into Active Surveillance, Passive surveillance and Sentinel Surveillance, and disease specific surveillance. 

Sentinel Surveillance:

Case 1: BPKIHS,  is a sentinel surveillance center for Kalazar.

Why is it a Sentinel Surveillance center for Kalazar?

• It has commitment and willingness to remain as sentinel center for Kalazar
• It has all the laboratory diagnostic facilities to diagnose Kalazar
• It has skilled manpower doctors, nurses, paramedics required to manage/treat Kalazar cases
• It lies in Sunsari district, particular geographic area or population, and is near to the districts where the Kalazar is endemic 

What is it doing currently?

• It actively finds the cases in the community where kalazar is endemic: case detection
• It provides treatment for Kalazar and follow up
• (NOTE: BPKIHS could be sentinel surveillance centre for many other diseases)

With this example in background, we can clearly understand what sentinel surveillance is. It is a process of monitoring occurrence of particular conditions in a population or also a monitoring of disease occurrence in a specific cohort such as in a geographic area or population subgroup to estimate trends in a larger population. Always keep in mind that certain agencies are only selected as sentinel surveillance centre due to their capacities. 

Sentinel: a soldier or guard whose job is to stand and keep watch

Surveillance: close observation/monitoring

Like the way a soldier or guard is kept to monitor and check for anything for security in healthcare for certain diseases or risk factors, certain health centres are selected for surveillance of specified diseases and while doing so, that centre should meet all the prerequisites. 

Data collected in a well-designed sentinel system can be used to signal trends, identify outbreaks and monitor the burden of disease in a community, providing a rapid, economical alternative to other surveillance methods. Because sentinel surveillance is conducted only in selected locations, however, it may not be as effective for detecting rare diseases or diseases that occur outside the catchment areas of the sentinel sites.

1. Centers for Disease Control and Prevention. Updated guidelines for evaluating public health surveillance systems: recommendations from the guidelines working group. MMWR Morb Mortal Wkly Rep 2001;50(RR-13):2.

2. Sentinel surveillance. Immunization,vaccine and biologicals. http://www.who.int/immunization/monitoring_surveillance/burden/vpd/surveillance_type/sentinel/en/

Lymphatic Filariasis: Challenges remains in Tropical Developing countries

Case Scenario

Case 1: In a Near by village 'Patnali' of Dharan municipality, we found a case of elephantiasis. she was very reluctant to talk about this chronic condition, however, after multiple visits during our family health exercise for MPH student, she started to give her details whatever she could recall.  she really didn't recall the exact time when she started having this sort of problem but she knew it was present when she was child and when she was aware of her physical appearance, she already had this disfigurement. Her reluctance to talk openly about it, is one of the indirect consequences of Filariasis. Importantly, she was also unaware of the the fact that this disease could be transmitted by the bite of mosquito. Patnali village lies in tropical region of Nepal, where the mosquitoes are endemic especially during Summer.

Case 2: I got an opportunity to meet a Female community health volunteer from the Prastoki, Duhabi the day after mass drug administration of Diethyl carbamazine Citrate and Albendazole. She shared that many people were reluctant to take the drugs as people feared of its adverse effects, they experienced last time. She , herself experienced adverse effects especially, dizziness and headache for one day following the ingestion of the drug.

Filariasis

Filariasis is one of neglected tropical diseases and remained as a public health challenge in certain districts of Nepal . It is caused by the parasite 'Wuchereria Bancrofti'. This is transmitted person to person by the vector 'Culex' mosquito. The adult worms only live in the human lymph system. Male worms are about 3–4 centimetres in length, and female worms 8–10 centimetres. The male and female worms together form “nests” in the human lymphatic system. Filarial infection can cause a variety of clinical manifestations, including lymphoedema of the limbs, Elephantiasis (A syndrome brought on from long-term obstruction of lymphatic vessels that leads to engorgement and thickened skin. It causes disfigurement, often of the leg.), genital disease (hydrocele, chylocele, and swelling of the scrotum and penis) and recurrent acute attacks, which are extremely painful and are accompanied by fever. The vast majority of infected people are asymptomatic, but virtually all of them have subclinical lymphatic damage and as many as 40% have kidney damage, with proteinuria and haematuria.

Transmission of Filariasis

Mass Drug administration of Diethyl Carbamazine Citrate (DEC) and Albendazole

Government of Nepal has brought the yearly mass drug administration (MDA) program of DiethylCarbamazine Citrate (DEC) and Albendazole since 2003 starting from Parsa district and this has been scaled up to all endemic districts of Nepal. 

Eligible population for drug ingestion: people residing in endemic area except pregnant women, children less than 2 years and seriously ill person. 

All districts should go through six rounds of MDA program by 2018 to achieve the national objective of eliminating lymphatic filariasis as public health problem by 2020. However, the major challenges is the noncompliance to the drugs. According to Annual report of Department of Health services, Nepal, in one fiscal year, among 18,900 people were interviewed it has been revealed an average of 57.9% drug ingestion against 68.9% reported coverage. Many people didn't take the drugs due to fear of adverse effects such as dizzines, Headache, GI disturbances, anorexia.  This non-compliance is partly also because of inability to convey the relevance of the ingestion in breaking the chain of transmission. As the people are free of signs and symptoms of filariasis, there is high chance that they won't feel necessity of its ingestion. Immunological disturbances can be induced by disintegrating microfilariae and dead adult worms. The incidence and severity of these reactions are correlated both with the degree of microfilaraemia and with the dose of diethylcarbamazine. Such adverse effects, immunological disturbances and relevance should have been covered highly before mass drug administration. 

Why we don't treat only the infected one  in the community

People living in filaria endemic areas, who look healthy, may be carrying microfilaria (mf) in their blood without any recognizable symptoms at the initial stage and finding the infected persons at this stage and giving them alone treatment is demanding. DEC kills mf and some adult worms and albendazole normally clears other intestinal worms which is an added benefit. When both the drugs are given together, it has effect on adult worms too and therefore the parasites will be destroyed preventing the infected person from becoming a source of parasites in the future. When every individual in the community takes drugs under MDA, microfilaria will be cleared and not present in the blood for the mosquitoes to transmit.

Even though the mass drug administration initiative is very purposeful and has fair coverage, strategies to increase its compliance and coverage is needed to achieve the national goal of making Nepalese people free of risk of filarial disease transmission.

Sources:

Annual Report 070/71. DOHS. MOHP

Diethylcarbamazine. http://apps.who.int/medicinedocs/en/d/Jh2922e/3.5.html  

Future: No oral polio vaccine in Nepal

Polio is a highly infectious disease, which is caused by a virus that invades the nervous system and causes paralysis. The virus is transmitted through person to person, mainly through the faecal-oral route.  Polio caused many deaths, morbidity and lifelong disability in the past and we can see traces of its fatal consequences as many deformed and paralyzed people in the villages of Nepal. However, the introduction of oral polio vaccine and its widespread coverage led to the reduction of its incidence and following fatal consequences. It is indeed a boon to mankind.

The Global Polio Eradication Initiative was launched in 1988. Since then oral polio vaccine has been used in the regular mass immunization. Oral Polio vaccines are available in different formulations.

OPV is available in different formulations:

·         Trivalent OPV – containing type 1, 2 and 3 serotypes

·         Bivalent OPV – containing type 1 and 3 serotypes

·         Monovalent OPV – containing one serotype (ie type 1, 2 or 3)

- See more at: http://www.polioeradication.org/Posteradication/OPVcessation.aspx#sthash.sC1ka2JW.dpuf

1.  Trivalent OPV: containing serotypes 1, 2, and 3
2.  Bivalent OPV: containing serotypes1, and 3
3.  Monovalent OPV: containing one serotypes (type1 or type 2 or type 3)

OPV is available in different formulations:

·         Trivalent OPV – containing type 1, 2 and 3 serotypes

·         Bivalent OPV – containing type 1 and 3 serotypes

·         Monovalent OPV – containing one serotype (ie type 1, 2 or 3)

- See more at: http://www.polioeradication.org/Posteradication/OPVcessation.aspx#sthash.sC1ka2JW.dpuf

OPV is available in different formulations:

·         Trivalent OPV – containing type 1, 2 and 3 serotypes

·         Bivalent OPV – containing type 1 and 3 serotypes

·         Monovalent OPV – containing one serotype (ie type 1, 2 or 3)

- See more at: http://www.polioeradication.org/Posteradication/OPVcessation.aspx#sthash.sC1ka2JW.dpuf

OPV is available in different formulations:

·         Trivalent OPV – containing type 1, 2 and 3 serotypes

·         Bivalent OPV – containing type 1 and 3 serotypes

·         Monovalent OPV – containing one serotype (ie type 1, 2 or 3)

- See more at: http://www.polioeradication.org/Posteradication/OPVcessation.aspx#sthash.sC1ka2JW.dpuf

OPV is available in different formulations:

·         Trivalent OPV – containing type 1, 2 and 3 serotypes

·         Bivalent OPV – containing type 1 and 3 serotypes

·         Monovalent OPV – containing one serotype (ie type 1, 2 or 3)

- See more at: http://www.polioeradication.org/Posteradication/OPVcessation.aspx#sthash.sC1ka2JW.dpufsome time line

There has been drastic improvement in the incidence of polio and paralysis and disability. There has been
Eradication of  Polio strain 2- 1999
Eradication of polio strain 3 - 2012

Inactivated polio vaccine (IPV) -since August 2014:
Inactivated polio vaccine was introduced on August 2014 in Nepal with the recommendation from National committee on Immunization Practices (NCIP). IPV is scheduled in 14 weeks of age after the birth of child until one year. IPV is produced from wild-type poliovirus strains of each serotype that have been inactivated (killed) with formalin. It is not a live vaccine and carries no risk of vaccine induced polio paralysis. The IPV induces low level of immunity in the intestine in comparison to oral polio vaccine and there is chance of multiplication of wild polio virus in the intestine and spread in the community. however, if the virus is contained in the community, there is less chance of contraction and furthermore spread making IPV effective. Though one dose IPV is given in Nepal as a complementary to current polio immunization, generally three spaced doses are administered to generate adequate levels of seroconversion, and most countries, a booster dose is added during late childhood.

IPV induces very low levels of immunity in the intestine. As a result, when a person immunized with IPV is infected with wild poliovirus, the virus can still multiply inside the intestines and be shed in the faeces, risking continued circulation.

Switch to bivalent oral polio vaccine containing polio strains 1 and 3 from trivalent oral polio vaccine polio strains 1,2 and 3 in Nepal on April, 2016:

This switch is in fact a major step to eradication of polio virus as this is required to eliminate the rare risks of vaccine-associated paralytic polio (VAPP) and circulating vaccine -derived poliovirus (cVDPV). This accords with one of the objectives of the Polio Eradication and Endgame Strategic Plan 2013-2018, which furthermore recommends removal of all oral polio vaccines in the long term.The removal of Polio strain2 is indeed required as this has been eradicated back in 1999 from the general population. This surely will help in eliminating vaccine induced type 2 polio in the immunized children.
Looking at this trend We are surely going to escape oral polio vaccine in the future.

Sources:

Bivalent oral polio vaccine (bOPV). Global Polio eradication Initiative. http://www.polioeradication.org/Polioandprevention/Thevaccines/BivalentOPV.aspx 

Replacing trivalent OPV with bivalent OPV: A critical step in polio eradication. Immunizations, vaccines and Biologicals. http://www.who.int/immunization/diseases/poliomyelitis/endgame_objective2/oral_polio_vaccine/en/ 

UNICEF, WHO, MOHP (Nepal). Introduction of Inactivated polio vaccine in Nepal: A public health milestone for polio free Nepal. December 2015. http://www.who.int/immunization/diseases/poliomyelitis/endgame_objective2/inactivated_polio_vaccine/Documentation_on_IPV_Introduction_in_Nepal_Final_lightversion.pdf