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Management of Outbreaks
This section deals with the measures that can be implemented in case of outbreaks of virus infections. The following topics will be covered:-
Control of Outbreaks of Viral Gastroenteritis
A. Outbreaks in hospitals and institutions
Small outbreaks of viral gastroenteritis are common in hospitals, especially among paediatric wards where rotaviruses and adenoviruses are usually involved. Large outbreaks involving adult wards are rare and small round structured viruses (SRSVs) are more likely to be involved. In such an outbreak situation, steps should be taken at the same time to establish the cause, mode of spread and control of the outbreak simultaneously.
Detailed information about the outbreak should be obtained. In particular, any factors common to those affected should be determined, such as whether they have consumed the same type of food, are the wards served by the same medical teams or other personnel, are any health workers involved. Fresh faecal specimens should be collected from an affected patient as soon as possible to ensure the maximum chance for detecting the pathogen. Faecal specimens should be sent for bacteriological and parasitical examination as well as virological examination. As a quick screen, the specimens could first be examined for the presence of rotaviruses or adenoviruses by EIA. The specimens should then be examined by electron microscopy or RT-PCR for Norwalk-like viruses if available. Only a small proportion of the specimens processed would be expected to yield a positive result. However, this is sufficient evidence to implicate SRSV as the agent. Other diarrhoeal viruses are occasionally involved in outbreaks in adults including caliciviruses, astroviruses, rotaviruses and adenoviruses. Normal electron microscopy should have little difficulty in detecting these viruses.
Diarrhoeal viruses are mainly spread by the faecal-oral route, either through infected foods such as shellfish or through an infected food handler. However, other modes of transmission are thought to be possible, in particular through aerosol sprays set up by vomitus. Food could be contaminated by this means or the viruses could be inhaled by other persons. Norwalk-like viruses have in particular been associated with airborne transmission. It is essential to determine whether any particular food consumed within last 5 days may be responsible. Whether any food handlers had been taken ill with gastroenteritis before or during the onset of the outbreak, whether any health workers working in any affected ward(s) were taken ill as they may play a role in the transmission of the virus to other wards. The plotting of an epidemic curve would determine whether the outbreak is a single source outbreak or involve person to person transmission.
Personal hygiene for both staff and patients should be emphasized, particularly hand-washing. Prompt removal of vomitus and diarrhoea is important in order to reduce the chance of environmental contamination. Affected persons should be isolated or cohorted together and enteric precautions instituted. This may be difficult in large outbreaks where there are difficulties in providing adequate facilities and staff for isolating cases. Any staff taken ill should refrain from coming to work. Transfer of staff from ward to ward should be avoided since this may spread infection to other wards. Implicated foods are likely to have been contaminated by the food handler. Food handlers who developed gastrointestinal symptoms should not be allowed to work. A scrupulously high standard of personal hygiene should be enforced for food handlers. Adequate toilet and hand washing facilities should be available which are regularly serviced. Work surfaces should be thoroughly cleaned to remove any environmental contamination. Attempts should be made to rethink food-handling practices to try to reduce the amount of handling of cooked or uncooked foods. It may be wise to take high-risk foods such as salads and sandwiches until the outbreak is clearly at an end. There are clearly a lot of problems involved in controlling outbreaks of viral gastroenteritis in hospitals, in particularly those associated with Norwalk-like viruses where outbreaks can rapidly involve several different wards through person to person spread. Fortunately, such outbreaks usually terminate spontaneously in 7 - 14 days and rarely lead to severe illness, even in those who are elderly or immunocompromised.
B. Community Outbreaks
Outbreaks of viral gastroenteritis in the community usually involve adults, and Norwalk-like viruses or SRVs are by far the most likely agents to be involved. The majority of outbreaks involve food, in particular shellfish. The hazards of consuming shellfish are well known, especially those usually eaten uncooked such as oysters. Provided that the cooking process is correctly applied, there is no reason why molluscan shellfish cannot be rendered virologically safe. Non-shellfish food-borne outbreaks tend to involve food which tend to be handled extensively in the kitchen, such as salads and sandwiches, which suggest that a food handler is involved as the source. In some cases, several items are implicated whilst in others, it may not be possible to identify any association because multiple items are involved. It is thought that a food handler is infectious up to 48 hours after recovery. It has been assumed that the main means by which transmission occurs is by the faecal oral route involving poor hand hygiene. Another possibility is contamination of food by the airborne route through vomitus of an affected food handler or a waiter. Outbreaks involving potable water have been reported, with persons infected running into hundreds or even thousands. Outbreaks of Norwalk-like viruses have also been associated with swimming in lakes and swimming pools. It is thought that person to person transmission plays a important part in the maintenance of certain outbreaks such as those reported for successive voyages on cruise liners. Such instances may be due to heavy environmental contamination by vomitus and diarrhoea.
The first aspect of control must be to interrupt person to person transmission. This may be very difficult in view of the information emerging about airborne transmission. Prompt removal of vomitus and diarrhoea should reduce environmental contamination. Contamination of shellfish probably occurs as a result of culturing in sewage polluted areas. Re-siting of shellfish beds and/or reduction of sewage pollution are clearly the fundamental steps. Another alternative is to move shellfish to cleaner waters for several weeks to reduce the level of contamination. Consideration should also be given to the removal of viruses from sewage effluent by treatments such as chlorination, ozone or UV light. Properly cooked shellfish should pose no infection risk but this is not applicable to oysters which are often eaten raw. In the prevention of outbreaks caused by food handlers, the most important aspect is to have a system that ensures that food handlers who develop acute GI infection do not continue to work. They should be able to report such illness and take time off work without financial penalty. A scrupulously high standard of hygiene should be enforced for food handlers. The workplace must have adequate toilet and hand washing facilities that are regularly cleaned and serviced. It may be advisable to rethink food handling practices to try to reduce the amount of handling of cooked foods or foods which are eaten uncooked. It is advisable to reduce the chance of contamination of other foods by oysters
In the case of ongoing food-borne outbreaks, potentially contaminated items present in the kitchen such as salads or cakes should be removed. Work surfaces should be thoroughly cleaned and disinfected. It is important to ensure that food handlers taken ill be excluded from work for at least 48 hours after recovery. The problems posed in trying to control SRSV outbreaks have been demonstrated by incidents on cruise liners. The rapid turnaround between cruises, with regular influxes of new susceptible persons, has resulted in repeated outbreaks on successive cruises.
Prevention of Transmission of Blood-Borne Viruses from Medical Staff to Patients
Outbreaks of hepatitis B associated with eAg positive surgeons have been recognized regularly in the UK at the rate of around once a year. This is much higher than that reported for other industrialized countries and could reflect increased vigilance in the UK because of relatively low incidence. The surgeon involved in the majority of outbreaks was thought to be technically competent and had not reported by needlestick injuries. Revised guidelines were issued on HBV infection and health care workers in August 1993. The guidance requires that health care workers who perform "exposure prone procedures" should be vaccinated, that the immune response to the vaccine should be documented, that those with a post-vaccination titre of HBsAb of <10mIU/ml should be investigated further. Those found to be HBsAg and eAg positive should cease to perform exposure prone procedures. Operative procedures are described as exposure prone if there is a risk of injury to the health care worker, which result in the exposure of the patients open tissues to blood or body fluids of the worker. Typically, such procedures include surgical or dental operations in which the workers gloved hands may be in contact with sharp instruments, needles, and sharp tissues inside a patients open body cavity, wound, or confined anatomical space where the hand or fingertips may not be visible at all times.
1. Outbreak Investigation
An outbreak in the UK between 1992 and 1993 where an eAg positive cardiothoracic surgeon was involved in two clusters in two separate hospitals (four cases in the first hospital, and two cases in the second). He was not detected during investigation of the first outbreak because he provided a false specimen. He was only detected following investigation of the second outbreak when the specimens were obtained directly from the surgeon and other health workers involved. The two blood specimens, and a third which he provided earlier to an occupational health department were found to be from different individuals after haptoglobin and alpha-1 antitrypsin grouping. HBV from the six cases proved to be virtually identical to the source surgeon after comparison of the nucleotide sequences and subtyping of HBsAg (all were found to be adr, which was uncommon in the UK).
Patients upon whom the infected surgeon had performed an exposure prone procedure on were identified from hospital operating theatre records. The family doctors of the patients were asked to obtain blood specimens from the patient. A single blood was requested from patients who had been exposed more than 6 months earlier, and two blood specimens (within 3 months of exposure and at least after 6 months after exposure) were obtained from patients exposed more recently. When a patient was found to have serological markers of HBV infection, stored specimens from the patient before surgery were retrieved and tested in parallel. Partners of patients found to be infected were offered serological testing, and, if appropriate, HBV vaccine. Enquiries were made on the presence of any risk factors for HBV infection other than the operation. 18 out of 307 patients tested had serological evidence of recent infection (seroconversion demonstrated or the presence of anti-HbC IgM), of which nine were still HbsAg positive. However one of these patients had a HBV subtype (ayw) which was different from the infected surgeon and thus could not have acquired it from surgery. The other eight had sequences identical or virtually identical with the infected surgeon. Nine patients were determined to have acquired infection acquired at an undetermined time because they were anti-HbC IgM negative and no pre-operative specimen was available. Therefore it could not be ruled that these patients may have acquired HBV infection from surgery. Seven patients were demonstrated to have been infected before surgery. Overall, the rate of transmission to susceptible patients was about 6%.
Tightening of guidelines - as a result of the lessons learnt from the above outbreaks, it is now recommended that when investigating a case of acute hepatitis B in a patient who had undergone surgery in the six months before becoming ill, blood specimens should be obtained from all members of the surgical team even if occupational health records are available. Furthermore, blood specimens from health workers should be obtained by directly observed sampling and tested for HBsAg. Molecular biology techniques may play a useful role in determining the source of infection.
2. Hepatitis B
The introduction of the Department of Health guidelines on HBV infection in health care workers in 1993 led to all health workers undertaking exposure prone procedures being testing for immunity to HBV. Those who were not immune were tested for markers of HBV infection and re-vaccinated if negative. Two trainee surgeons employed by two district general hospitals in the same area were found to be eAg positive HBV carriers. Neither surgeon gave a history of injury at work. The surgeons were suspended from work, counseled, and further blood specimens were taken to confirm the diagnosis and for further investigation. An infection control team, made up of public health physicians, a virologist, a surgeon, and hospital chief executive was convened. The surgeons were examined carefully by the occupational health department to assess the risk of occupational transmission, such as injuries at work, history of jaundice or hepatitis, chronic skin lesions, injecting drug, overseas work, past vaccination, received dental treatment or other operations.
The patient administration system of the hospital was asked to identify all patients that the surgeons had operated on. Patients were counseled individually at home, and blood taken for HBV testing. Patients operated on within 8 weeks earlier were given an accelerated course of vaccine (0, 1, 2, and 12) in the hope that, even if infection had already occurred, severe illness and the development of a carrier state might be prevented. The family doctors of the patients were informed of the management decision and were asked to provide another blood specimen six months after the operation. A press statement was released without giving any personal details about the surgeons or their patients. However it described how long the surgeons had been employed, why they were tested, and at what hospitals the surgeons had worked at. The statement also stated that the surgeons had stopped operating and that all their patients had been counseled. Two of the sixteen patients on whom one of these surgeons had performed exposure prone procedures were shown to have acquired infection from that surgeon. The HBV nucleotide sequences were shown to be identical to the source surgeon by single stranded conforma3tion polymorphism (SSCP). The partners of these patients were also counseled and given HBIG and vaccine.
To date, there has only been a single report concerning the transmission of HIV infection to 5 patients by a Florida dentist. The mechanism of this transmission remains speculative as the dentist died before his techniques could be verified. It is not possible to quantify the risk of transmission from health care worker to patient, but it must be extremely low given that large volumes of blood would need to enter the patients bloodstream. The GMC recommends that all staff who think that they have been at risk of infection should be confidentially tested for HIV infection. Testing for HBV and possibly HCV should also be encouraged. Should HIV infection be detected, counseling and expert advice should be sought. If the health care worker is HIV or eAg positive, then he should stop performing invasive procedures i.e.
Should a health worker who had performed invasive procedure be found to be HIV-positive. Enquiries should be made to determine the possible risk of him having transmitted his infection to patients, such as whether he had sustained any injuries while operating, chronic skin lesions etc. The procedures and the role he played in them should be reviewed. It may be advisable to trace those patients, counsel them and offer anti-HIV testing. Postexposure prophylaxis would not be indicated given the very low risk and also the fact that it is probably ineffective after 36-48 hours.
4. Hepatitis C
Although not as infectious as HBV, there had been reports of HCV infection transmitted from infected surgeon to patient. Although, there are no clear guidelines at present, it is likely, that HCV positive surgeons will be asked to refrain form performing exposure-prone procedures as in the case of HBV and HIV positive surgeons. There are no indications for mass screening of surgeons. Instead, those who are at increased risk should be encouraged to come forward for HCV as well as HIV and HBV testing and counseled if found to be positive.
Outbreaks of Respiratory Virus Infections
In general, patients with respiratory virus infections should be isolated in single cubicles or cohorted with respiratory precautions. The room should be under negative pressure. Gloves and gowns (or plastic aprons) should be worn on entering the room. The value of filter masks is highly debatable, but should be worn when handling the patient. Hand washing must be carried out on leaving the room. The number of staff attending the patient should be restricted. Disinfection of surfaces may be carried out by 1000 ppm hypochlorite. Viruses under this category include varicella-zoster, measles, mumps, rubella, parvovirus, influenza, parainfluenza, and RSV. Where possible, nursing of patients should be carried out by staff known to be immune eg. for VZV, mumps, measles, and rubella. For this reason, It would be invaluable to have a record of staff immunity to childhood illnesses kept either by the sister in charge or by the occupational health department.
Outbreaks of chickenpox is of particular concern in wards with immunocompromized patients, particularly paediatric oncology wards with leukaemic children, adult oncology wards, and bone marrow transplant recipients. It is also of concern in obstetric wards and neonatal wards. In the case of obstetric wards, the main concern is that chickenpox is likely to be more severe in pregnant women, and therefore, if supplies permit, susceptible women should be given ZIG. Any baby born whose mother developed the rash of chickenpox within 7 days of delivery should also be given ZIG and possibly acyclovir. Acyclovir is thought to be safe for the fetus. The following are guidelines for dealing with potential contacts of chickenpox in susceptible wards.
Measles outbreaks are most deleterious in wards with immunocompromised children or adults e.g. children with leukaemia and BMT patients. Measles is definitely as dangerous as VZV in that setting. Measles can cause severe disease in babies who are undernourished, immunocompromised, or suffering from chronic debilitating disease. Therefore babies with the above conditions, or who had recently recovered from a severe illness should be protected by HNIG.
Prevention of the nosocomial spread of RSV infection is of prime importance, as many hospitalized infants have underlying conditions which make them susceptible to severe RSV infection. A number of hospital outbreaks of RSV infection have been described in infants, the immunosuppressed, and the elderly.
Influenza is a particularly worrying problem in nursing homes where individuals with chronic debilitating disease are especially susceptible to severe life-threatening influenza infection.
Despite the vaccination program, a small proportion of women of childbearing age is still susceptible to rubella. Therefore, outbreaks of rubella occurring in hospital wards or outpatients affecting susceptible pregnant women is still a possibility.
Outbreaks of Enteric Viral Infections
1. Diarrhoeal Viruses
Most admissions from the community for viral diarrhoea, other than in a food-related outbreak, occur in winter usually in children under 3 years old. Rotavirus account for over 50% of episodes of acute viral diarrhoea in children.
Since the advent of polio vaccination, the majority of reported cases of paralytic poliomyelitis were due to vaccine strain virus. However, cases of paralytic poliomyelitis are still reported from time to time.
3. Coxsackie and Echoviruses
In normal wards, enteric precautions would be sufficient after the diagnosis of a coxsackie or echovirus infection, paying particular attention to hand washing, disinfection of surfaces with hypochlorite 1000 ppm, heat disinfection of bedpans and instruments. However, coxsackie or echoviruses may cause severe problems in a neonatal ward.
4. Hepatitis A
Control of Viruses that Spread by Direct Inoculation
Outbreaks of HSV infection have been described in neonates which were confirmed by DNA fingerprinting.
Nosocomial outbreaks of adenovirus pneumonia and URTI, especially caused by types 3 and 7, have been described, as have epidemic conjunctivitis.
There is no evidence that CMV is acquired nosocomially. Studies in hospital nurses caring for children have not shown any evidence of increased infection rates when compared with women of similar ages working in other occupations. Nonetheless, it would seem prudent to minimize the risks of cross-infection by careful attention to infection control measures in any patient known to be excreting CMV. Gloves and aprons should be worn and careful hand washing implemented. In case of pregnant women in contact with known CMV excretors, the following should be advised.
Management of Rabies
Rabies is an acute viral infection resulting in encephalomyelitis and almost invariably in death. The incubation period is usually between 2 to 8 weeks (range 9 days to 2 years). Infection is usually through the bite of a rabid animal. Rarely, transmission of the virus can also occur through mucous membranes. Person to person spread of the disease is extremely rare but there had been instances of transmission through corneal grafts.
Pre-exposure prophylaxis should be offered to all those whose work may lead to potential contact with rabid animals. It should be given to all health workers caring for a patient with confirmed or suspected rabies. Three 1 ml doses (0, 7, 28) by deep subcutaneous or i.m, is normally used. The vaccine may also be given in smaller doses by the intradermal route (0.1 ml) with the same intervals. The intradermal route may also be used for the rapid immunization of staff caring for a patient with rabies by giving 0.1 ml into each limb (0.4 ml in all) on the first day of exposure to the patient. Intradermal immunization is only reliable if the whole of the 0.1 ml dose is given into the dermis and should only be given by a person experienced in the technique. The use of the intradermal route is not covered by the manufacturers license. Booster doses of the vaccine should be given every 2 to 3 years. The three-dose course gives virtually 100% protection and thus routine post-immunization testing is unnecessary. However, serological testing is advised for those who work with live virus and this should be carried out every 6 months.
In the event of a possible exposure, the following protocol should be observed in the UK;-
Management of patient diagnosed or suspected of having rabies
Viral Haemorrhagic Fever
In Africa, transmission of VHF has been associated with the reuse of unsterile needles and syringes and inadequate barrier nursing procedures for blood, other body fluids, secretions and excretions. The risks associated with various body fluids have not been well defined as most caregivers who acquired infection had multiple contacts with multiple fluids. The exact risk of airborne transmission is uncertain but must be very low, since to date, no cases of airborne infection involving humans had been documented. However this must be considered to be a possibility especially in patients with advanced stages of disease. Moreover, airborne transmission of VHF had been demonstrated in monkeys. The risk of person-to-person transmission is highest in the latter stages of the illness, which are characterized by vomiting, diarrhoea, shock, and haemorrhage. VHF infection has not been reported in persons whose contact occurred during the incubation period, the incubation period generally ranging from 2 days to 3 weeks.
The WHO made recommendations in September 1995 for management of suspected cases of viral haemorrhagic fever. These recommendations apply to patients who, within 3 weeks before the onset of fever, either (1) traveled in the specific local area of a country where VHF has recently occurred, (2) those who had direct contact with the blood, other body fluids, secretions or excretions of a patient or animal with VHF, (3) worked in a laboratory or animal facility that handles haemorrhagic fever viruses. The likelihood of acquiring VHF is considered to be extremely low in persons who do not meet any of the criteria.
Summary of Infection Control Measures
|Virus||Incubation Period||Duration of Infectivity||Prophylaxis||Antiviral Treatment|
|Measles||7-14 days||4 days before to 2 days after rash appears||HNIG and vaccination||Possibly ribavirin|
|Varicella||10-21 days||4 days before to 5 days after rash appears||ZIG and vaccination||Acyclovir, famciclovir,|
|Zoster||5 to 7 days after rash appears||Acyclovir||Acyclovir and valaciclovir|
|Mumps||14-24 days||2 days prior to and 4 days after parotitis appears||Vaccination||None|
|RSV||3-7 days||3 days prior to onset of symptoms to cessation of symptoms||None||Ribavirin|
|Influenza||1-4 days||1 day before to 4 days after onset of symptoms||Vaccination,
Amantidine (flu A), zanamivir
|Amantidine (flu A), zanamivir|
|Parainfluenza||3-8 days||3 to 10 days||None||None|
|Rubella||14-21 days||7 days before to 10 days following rash||Vaccination, ?HNIG||None|
|Parvovirus||6-8 days||10 days prior to appearance of the rash||HNIG||HNIG|
|Rotavirus||1-3 days||Adults for
duration of symptoms
Children up to 5 days after end of symptoms
|Other diarrhoeal viruses||up to 48 hours||24 to 48 hours||None||None|
|Enterovirus||2-35 days||3-4 days prior to and up to 2 weeks after symptoms||Vaccination (polio)||HNIG|
|Hepatitis A||2-6 weeks||3 weeks prior to onset to 1 week after onset of jaundice||HNIG
|Herpes Simplex||2-11 days||Primary infection 3-4 weeks, secondary infection 3-5 days||Acyclovir||Acyclovir,
|Adenovirus||5-10 days||up to 10 days following onset of symptoms||None||None|
|Hepatitis B||2-6 months||Variable||HBIG, vaccination||interferon, 3TC|
|HIV||up to 6 months before seroconversion||Lifelong||AZT+ other agents||AZT and other agents|
|Hepatitis C||5-10 days||Variable||None||Interferon, ribavirin|
|VHF||2-21 days||14 days following onset of symptoms but may be as long as 2 months||Ribavirin||Ribavirin|
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