A LABORATORY ERROR

A CASE OF LABORATORY ERROR

The story:

An interesting and serious problem arose in the hospital over the past two months.

The father of one of the children in the children's ward  had had a persitent cough for the last two weeks. He visited on a daily basis. He was reluctant to go to the local health centre because he was busy harvesting his maize crop.  He was told he must have a sputum sample tested before he could visit again. Our senior laboratory technician was on leave, but the junior technician said he had been trained to perform ZN staining on a sputum sample.

A sputum sample was obtained, and processed in the laboratory. The technician saw the following down the microscope:

For answers to questions: See previous post: Answers to Lab Error Questions.

  

QUESTION 1:

This is a ZN stain of the sputum. What is seen on the slide?

The story continued:

The father had only visited his child in the ward, and had not been close to other children. His child, who was six years old, had had a BCG vaccination soon after birth. The father was referred to the TB clinic at the local hospital, and told he should not visit the unit until he had been on treatment for two weeks.

QUESTION 2:

From the above information, is it likely that any patients or staff in the ward were at risk of aquiring TB infection from the father? If so, give three points for action.

Five weeks later:

Five weeks after the incident, the laboratory cleaner did not report for work for a few days.  Her daughter brought a note saying that she had a fever and a bad cough. The previous night, the daughter said there was blood in the sputum. Four days later, her condition worsened and she was taken to the local hospital. The hospital laboratory examined s sputum sample and found it acid fast bacilli positive, and a diagnosis of pulmonary tuberculosis was made. Several staff remembered the cleaner, who also cleaned in the children's unit, had had a cough for about a week  before she took sick leave.

QUESTION 3:

TB is not uncommon among adults in this area, so it may be there is no link between the two cases. HOWEVER, do you have any suggestion how there may be a link between the two cases?

A third case occurs:

Two weeks later, the laboratory aid (who is responsible for cleaning the benches and discarding specimens) became unwell with fever and a cough. She attended the local health centre and a sputum sample wsas sent to the laboratory at the district hospital. It was found to be acid fast bacilli positive.

The children's ward sister is now concerned that somehow the ward or the laboratory was the source of infection in the cleaner and lab aid, and an investigation is begun.

Investigating an incident such as this has two main components:

a). To look for, and explain, epidemiological links between the cases

b). To investigate the processing of the specimen in the laboratory.

Had the lab aid or the cleaner come into contact with the first case?

There was no evidence that either the cleaner or the lab aid ever came into contact with the first case. It was therefore decided to investigate whether a breakdown in protocol had occurred in the laboratory, resulting in infection from the sputum sample.

These were the findings:

• the junior laboratory technician had performed ZN staining correctly and had worn a mask while handling the specimen
• the junior technician was busy with other tasks to do, and had left the specimen on the bench, rather than discarding it or putting in the refrigerator for storage
• when the lab aid cleaned the bench the following morning, she accidently knocked the specimen pot on the floor, which cracked and the lid fell off.
• the cleaner, who was in the laboratory at the same time, helped the lab aid to clean up the sputum, and rinsed the pot under a tap

QUESTION 4:

From the above findings, can you explain how and why the lab aid and the cleaner may have become infected?

The follow up:

Following the results of the investigation, a meeting was held with all the staff involved. The following actions were decided:

• The protocol for processing sputum specimens for ZN staining must be checked to ensure correct disposal of specimens is clearly described
• The junior technician to undergo a supervised programme with the senior laboratory technician for all laboratory activities and demonstrate his competence in the work
• Arrangements made for the temporary replacement of the lab aid and cleaner while they are on sick leave
• A  monitoring system set up to regularly audit the sputum processing in the laboratory
• The clinical staff are reminded to note any children in the t who develop a cough or fever to be referred to the paediatrician at the local hospital
• All staff told to report to a senior staff member if they develop a cough or unwell.

Both the lab aid and the cleaner made good progress on TB treatment, and fully recovered.

This episode was a useful experience: if even a small component of a laboratory protocol is not followed, serious infection hazards can result.

For the Medcare  programme, Uganda, the infection risk assessment proforma can be used to review the issues in this scenario.

The following link is to the form, with entries based on this case study:

Lab infection investigation form

Further reading on laboratory acquired infection:

1. TB risk among staff in a large hospital in Kenya. Int Jl TB and Lung Disease, 2008;12:949-954.

Free download at:http://www.ingentaconnect.com/content/iuatld/ijtld/2008/00000012/00000008/art00013?token=00511b8458b52781cca7b76504c48662a252c495b6c5f737b2d356a332b25757d5c4f6d4e227aaa5e

2. WHO Laboratory Bio-safety Manual.

Free download at: http://www.who.int/csr/resources/publications/biosafety/WHO_CDS_CSR_LYO_2004_11/en/

ANSWERS TO LAB ERROR QUESTIONS

ANSWERS TO THE QUESTIONS ON THE LABORATORY ERROR POST

QUESTION 1:

This is a ZN stain of the sputum. What is seen on the slide?

Pink bacilli (rod shaped bacteria), these are acid fast bacilli, typical of mycobacteria. While the sputum would have to be cultured to confirm the diagnosis, it is probably Mycobacterium tuberculosis.

QUESTION 2:

From the above information, is it likely that any patients or staff in the ward were at risk of acquiring TB infection from the father? If so, give three points for action.

The father is sputum positive, that means he is infectious with TB, and could infect anyone (patients or staff) who is susceptible, and who was close to him when he was coughing.

Action points could include the following:

§         Check if any children on the ward had not had BCG. Advice from the district TB officer should be sought. This would be particularly important if any child was known to be HIV positive, or had other reason for reduced immunity

§         All staff should be told to inform the senior hospital nurse if they develop a cough or become otherwise unwell

§          

QUESTION 3:

TB is not uncommon among adults in this area, so it may be there is no link between the two cases. HOWEVER, do you have any suggestion how there may be a link between the two cases?

The possible links (but we do not know the answers yet) could be:

a). The lab aid and the cleaner were both on the children's ward at various times when the father was there, and so became infected from him,

b). There may be no link, either with the father or the hospital. Both could have been infected in the community,

c). They may both have been exposed to infection in the laboratory.

QUESTION 4:

From the findings, can you explain how and why the lab aid and the cleaner may have become infected, but not the junior technician?

(These were the findings:

• the junior laboratory technician had performed ZN staining correctly and had worn a mask while handling the specimen
• the junior technician was busy with other tasks to do, and had left the specimen on the bench, rather than discarding it or putting in the refrigerator for storage
• when the lab aid cleaned the bench the following morning, she accidently knocked the specimen pot on the floor, which cracked and the lid fell off.
• the cleaner, who was in the laboratory at the same time, helped the lab aid to clean up the sputum, and rinsed the pot under a tap)

The junior technician wore a mask while processing the specimen, and apart from not discarding the specimen correctly, appears to have followed the correct protocol.

Both the lab aid and the cleaner were exposed to infectious material when the specimen pot fell and cracked, and in the process of cleaning up.